Chapter I: Colours Derived From Aniline and Toluidine

_Blues and Violets._

Mauve, aniline purple, Perkin’s violet, violine, mauve, rosaniline,
anodising, &c.

Aniline blue, rosaniline blue, Hofman’s blue, bleu de Paris, bleu de
Lyons, bleu de Mulhouse, bleu de Mexique, bleu de nuit, bleu lumière,
night blue.

Hofman’s blue.
Nicholson’s blue, soluble blue.
Hofman’s violet, rosaniline violet.

A long series of red and blue violets, bearing Hofman’s name and
distinguished in commerce by adding R or B, according to the redness or
the blueness of the tint, ranging from RRRR to BBBB.

Dahlia.
Toluidine blue.
Violet de Paris.
Mauvaniline.
Violaniline.
Regina blue, opal blue, bleu de Fayolle, violet de Mulhouse.
Britannia violet.
Violet imperial.
And many others.

_Reds._

Aniline red, new red, magenta, solferino, aniline, rougé, roseine,
azaline.
Rubine, rubine imperial.
Chrysaniline red.
(_The above are all salts of rosaniline_)
Xylidine, tar red, soluble red.

_Yellows._

Chrysaniline, phosphine, aniline yellow, yellow fuschine.
Chrysotoluidine.
Dinaline.
Field’s orange.

_Greens._

Aldehyde green, aniline green, viridine, emeraldine.
Iodine green, iodide of methyl green, iodide of ethyl green.
Perkin’s green.

_Browns._

Havanna brown.
Bismarck brown, aniline brown, Napoleon brown, aniline maroon.

_Greys and Blacks._

Aniline grey, argentine.
Argentine black.

II.—COLOURS DERIVED FROM PHENOL.

_Blues and Violets._

Isopurpuric acid, Grénat.
Azuline, azurine.

_Reds._

Picramic acid.
Coralline, peonine.
Red coralline.

_Yellows._

Picric acid, carbazotic acid.
Aurine, rosolic acid.

_Green._

Chloropicrin.

_Browns._

Picrate of ammonia.
Isopurpurate of potash.
Phenyl brown, phenicine.

III.—COLOURS DERIVED FROM NAPHTHALENE.

_Reds._

Pseudoalizarine, naphthalic red.
Roseonaphthaline, carminaphtha.

_Yellows._

Binitronaphthaline, naphthaline yellow, golden yellow, Manchester
yellow.
And others.

The introduction of aniline colours into dyeing and calico-printing has caused quite a revolution in these arts, the processes having become much more simple, and the facilities for obtaining every variety of tint largely increased. The arts of lithography, type-printing, paper-staining, &c., have also profited by the coal-tar colours. For such purposes the colour is prepared by fixing it on alumina, a process in which much difficulty was at first experienced, for the colours are themselves almost all of a basic nature. The desired result is now attained by fixing them on the alumina with tannic or benzoic acid. These lakes produce brilliant printing-inks, which are extensively used. The aniline colours are also employed for coloured writing-inks, tinted soaps, imitations of bronzed surfaces, and for a variety of other purposes.

Not many years ago coal-tar was a valueless substance: it was actually given away by gas-makers to any one who chose to fetch it from the works. It was then “matter in the wrong place;” but Mr. Perkin’s discovery led to its being put in the right place, and it has become the raw material of a manufacture creating an absolutely new industry, which has developed with amazing rapidity. This industry dates from only 1856, and in 1862 the annual value of its products was more than £400,000. Dr. Hofman, in reporting on the coal-tar colours shown at the Paris Exhibition of 1867, computed the value at that time at about £1,250,000, although the products were much cheaper than before. Large manufactories have been established in Great Britain, in France, Germany, Switzerland, America, and other countries. The possibility of such an industry is an interesting illustration of the manner in which the progress made in any one branch of practical science may lead to unexpected developments in other quarters. The quantity of aniline obtained from coal-tar is very small compared to the amount of coal used, as may be seen from the following table, in which the respective weights of the various products required in the manufacture of _mauve_ are arranged as given by Mr. Perkin for the produce of 100 lbs. of coal.

lbs. oz.
Coal 100 0
Coal-tar 10 12
Coal-tar naphtha 0 8½
Benzol 0 2¾
Nitro-benzol 0 4¼
Aniline 0 2¼
Mauve 0 0¼

From this we may perceive that had not the manufacture of gas been greatly extended, so as to yield a large aggregate produce of tar, the requisite supply for the manufacture of aniline would not have been attainable; and the industrial application of the previously worthless bye-product reacts upon gas manufacture by cheapening the price of that commodity, thus tending still more to extend its use.

Although anthracene has already been named as one of the colour-producing substances found in coal-tar, we have not in the list of coal-tar colours included the colouring matter which anthracene is capable of yielding. The reason is that this case stands apart in some respects from the rest. The colours derived from aniline and the other substances already enumerated are instances of the production of bodies not found in nature—mauve, magenta, &c., do not, so far as we know, exist in nature. Their artificial formation was a production of substances absolutely new. The colour of which we have now to treat is, on the other hand, found in nature, and from its occurrence in the _rubia tinctoria_, the roots of that plant have for ages been employed as a source of colour, and are well known in this country as “madder.” The plant is grown largely in Holland, in France, in the Levant, and in the south of Russia.[18] Madder is used in enormous quantities for dyeing reds and purples: the well-known “Turkey red” is due to the colouring matter of this root. The total annual value of the madder grown is calculated to reach nearly 2½ million pounds sterling. More than forty years ago it was discovered that the madder-root yielded a colouring substance, to which the name of “alizarine” was bestowed, from _alizari_, the commercial designation of madder in the Levant. The alizarine does not exist in the fresh root, but is produced in the ordinary processes of preparing the root and dyeing with it, in consequence of a peculiar decomposition or fermentation. Alizarine may be procured from dried madder by simply submitting it to sublimation, when beautiful orange needle-shaped crystals of alizarine may be obtained. It is nearly insoluble in water, but readily dissolves in hot spirits of wine. Acids do not dissolve it, but potash dissolves it freely, striking a beautiful colour; with lime, barytes, and oxide of iron, it forms purple lake, and with alumina a beautiful red lake. According to Dr. Schunck, of Manchester, to whose investigations we are indebted for much of our knowledge of madder, the root contains a bitter uncrystallizable substance called “rubian,” which, under the action of certain ferments, and of acids and alkalies, is decomposed into a kind of sugar, and into alizarine and other colouring matters. The ferment, which in the process of extracting the colouring matter from the roots causes the formation of alizarine, is contained in the root itself.

Footnote 18:

The natural Order to which the madder plant belongs is interesting
from the number of its members which supply us with useful products.
That valuable medicine, quinine, is obtained from plants belonging to
this family, as is also ipecacuanha, and other articles of the
_materia medica_. _Coffea arabica_, which furnishes the coffee-berry,
is another member.

We have already seen how an investigation relating to a question of pure chemical science accidentally led Mr. Perkin to the discovery of mauve—the precursor of the long range of beautiful colours already described. The mode of artificially preparing alizarine, so far from being an accidental discovery, was sought for and found in 1869 by two German chemists, Graebe and Liebermann. The researches of these chemists were conducted in a highly scientific spirit. Instead of making attempts to produce alizarine by trying various processes on first one body, then another, to see if they could hit upon some tar product, or other substance, which would yield the desired product, they began by operating analytically on alizarine itself. Just as a mechanic ignorant of horology, required to make a watch, would be more likely quickly to succeed in his task by taking a watch to pieces to see how it is put together, than if he had tried all manner of arranging springs and wheels until he hit upon the right way; so these chemists set themselves to take alizarine to pieces, in order to see from what materials they might be able to put it together. They decomposed alizarine, and among the products found a hydro-carbon identical in all its properties with _anthracene_.

Anthracene was discovered in coal-tar by Laurent in 1832, and its properties were investigated by Anderson in 1862. It may be remarked that such investigations were not conducted with a view to any industrial uses of anthracene, but merely for the sake of chemistry as a science. Certainly no one could have supposed at that time that the slightest relation existed between anthracene and madder. Anthracene is a white solid hydro-carbon, which comes over only in the last stages of the distillation of coal-tar, accompanied by naphthaline, from which it is easily separated by means of spirits of wine, by which the naphthaline is readily dissolved, but the anthracene scarcely. Anderson, in 1861, discovered, among other results, that anthracene, C_{14}H_{10}, by treatment with nitric acid became changed into oxy-anthracene, C_{14}H_{8}O_{2}; and this reaction we shall see is a step in the process of procuring alizarine from anthracene. Phenol, as already mentioned, can be made to yield benzol, by a process of deoxidization. With a view to similarly obtaining a hydro-carbon from alizarine, Graebe and Liebermann passed its vapours over heated zinc filings, and thus produced anthracene from alizarine. It now remained to find a means of reversing this process, that is, so to act on anthracene as to produce alizarine, and this was effected by treating anthracene with bromine, forming a substance which, on fusing with caustic potash, yielded _alizarate of potash_, from which pure alizarine resulted by treatment with hydrochloric acid. A much cheaper method was, however, necessary for manufacturing purposes, and it was found in a process by which oxy-anthracene, C_{14}O_{8}H_{2}, is treated at a high temperature with strong sulphuric acid, and the product so formed heated with a strong solution of potash, yielding alizarate of potassium as before. Many other interesting substances appear to be formed in the reactions, but the nature of these bodies has as yet been imperfectly investigated. No doubt whatever can be entertained of the identity of natural with artificial alizarine; and the production of this substance, the first instance of a natural colouring matter made artificially, may be regarded as a great triumph of chemical science. It was not long ago supposed that the chemical bodies found in plants or animals, or produced by vital actions, could not possibly be formed by any artificial process from their elements. The laws which presided at their formation were, it was conceived, wholly different from those which governed the chemicals of the laboratory, for they were held to act exclusively under the influence of a mysterious agent, namely, “vital force.” It was supposed, for example, that from pure carbon, oxygen, and hydrogen, no chemist would ever be able to produce such a compound as acetic acid. Accordingly the domain of chemical science, previous to the end of the first quarter of the present century, was divided by an impassable barrier into the two regions of organic and inorganic chemistry. Now, however, the chemist is able to build up in his laboratory from their very elements a great number of the so-called _organic_ bodies. And it is quite possible to do this in the case of alizarine; that is, a chemist having in his laboratory the elements, hydrogen, carbon, oxygen, &c., could actually build up the substance which gives its value to madder.

The quantity of anthracene procurable from coal-tar is, unfortunately, comparatively small, for it is found that from the distillation of 2,000 tons of coal only one ton of anthracene can be obtained. The use of artificial alizarine would doubtless entirely supplant the employment of madder-root if anthracene could be obtained in larger quantities; and the change would be highly advantageous to this country, for as no madder is grown in Great Britain, and we consume nearly half the whole annual growth, it follows that every year a million pounds sterling go out of the country for this commodity. When anthracene is produced from coal in sufficient abundance, this sum will be available for the support of our own population. In the meantime, the manufacture of artificial alizarine is restricted only by the supply of its raw material.

The foregoing paragraphs of the present article, which were written for the first edition of this work, not long after the introduction of artificial alizarine, require some supplementary reference to the subsequent progress of discovery and to the increased importance of the manufacture of the coal-tar colours on the large scale. Since the first introduction of alizarine as a commercial product, the substance has received much attention from chemists. The constitution of the body called above _oxy-anthracene_ is now better understood, and its chemical relationship is more clearly indicated by the systematic name of _anthraquinone_, which it now bears. The process of the manufacture of alizarine has received some advantageous modifications, and the artificial product may now be said to have entirely displaced the madder-root in dyeing. But, more than this, chemists have found means of preparing a number of “derivatives” of alizarine, many of which are either colouring matters or are easily converted into such. Nearly thirty of these substances have been described, and several of them have found extensive industrial applications. We may mention _alizarine blue_, C_{17} H_{9} NO_{4}, and another substance, produced by combining that with _sodium bi-sulphite_, and having the formula C_{17} H_{9} NO_{4} 2Na H SO_{3}. This last, manufactured largely, and sold under the name of “_alizarine blue S._,” is remarkable for being one of the most permanent of all colouring matters. It is said to be a faster colour than even indigo blue, which, indeed, it is rapidly replacing in dyeing, where it is applicable to cotton with a chromium mordant and to silk with one of alumina. Two other colouring matters have also been derived from anthracene, and are much used in dyeing; one is commercially named _anthracene purple_, the other is _anthracene green_, which supplies the calico printer with very fast shades of olive-green.

Several of the substances enumerated in the list of coal-tar colours, in pages 689 and 690, are now but little used, or altogether abandoned in dyeing and calico printing, because either their beautiful hues prove too fugitive, or other bodies of the same class can be produced at a much cheaper rate. The range of choice is now of the amplest, for chemical discovery has been wonderfully active, but in many cases the real nature and relationship of the artificial colouring matters enumerated above have only quite recently been made out. Mauve (now called _rosaline_), for example, the oldest of all the colour-tar colours, and one which, as we have seen, was manufactured on an extensive scale many years ago, is now scarcely made at all, because much cheaper violets have taken its place. The science of the tinctorial substances has lately taken a much more distinct form, and this knowledge has borne fruit for industrial purposes. It would be out of place here to review what has been done in this way, but a few facts will show the richness of the field. It was only in 1886 that the true chemical constitution of a class of coal-tar derivatives, called _azines_, was first made out. They present themselves as pale yellow or orange coloured crystallized solids, which melt at a comparatively high temperature and may be distilled without decomposition. Although highly coloured substances themselves, before they are converted into fast dyes they require further treatment, which introduces into their molecules another group of atoms. An almost indefinite number of such compounds are theoretically possible, but from only a very few of them many useful dye stuffs are now prepared on the large scale. Amongst the most important of these are “neutral red,” “neutral violet,” and two other violet colouring matters, “red dyestuff,” “fuchsia,” “giroflé,” “Magdala red,” “indazine” and “Basle blue.”

Among the colouring matters before enumerated are “aniline yellow” and “Bismarck brown.” Their real nature was not understood until a few years ago; and though the use of the aniline yellow itself has been abandoned on account of its fugacity, the substance has been found a most prolific parent, which has supplied dye stuffs of the most diverse and brilliant hues. These form what chemists term the _azo colours_, and they have been manufactured in great variety and on a very large scale. In 1876, the class of them called _chrysoidines_ was introduced, and again, in 1878, _tropœolines_. Great numbers of different azo colours have been sent into commerce under various names, such as “butter yellow,” “_crocein scarlet_,” “_Biebrich scarlet_,” “_Congo red_,” “_Bordeaux G._,” “fast red,” &c., &c. About 140 of these azo dyes have been described, and the commercial importance of this one class of compounds alone may be inferred from the fact of no fewer than 200 patents having been taken out for processes relating to their manufacture in the eleven years from 1878 to 1888.

It would not be difficult to fill this book with instances of the way in which the resources of modern life have been increased by chemistry alone, a science almost entirely the creation of the present century. Many of the processes of manufacture in which chemistry is applied to the production of articles of every-day use have been so often described, that they may be assumed to be already so well known as to offer few elements of novelty to the general reader, whose interest would also be likely to flag if he were carried over a long range of even the brilliant discoveries that are so delightful and instructive for the special students of this science. There is no parallel to the rapidity of the progress made by the younger branch of the science which concerns itself with the chemistry of one element—namely, carbon and its various combinations, and it is from these carbon compounds that our examples have been drawn. In the explosives, we have some of these compounds supplying resistless forces for rending rocks, and furnishing in warfare the most dreadful powers of destruction. In anæsthetics, we see beneficent applications of others in alleviating suffering and annulling pain; and again we have just shown how richly another set of them can minister to our sense of beauty. The discussion of these topics has afforded an opportunity for bringing before the reader some of the laws or summarized statements of experimental facts, and also some of those symbolical conceptions of the constitution of compounds, which together furnish the clues that guide the chemist through the vast labyrinth of the endless transformations of matter. The results attained show that the notions expressed by such words as _atom_, _molecule_, _compound radical_, _structural formula_, etc., have a true representative correspondence with something in the actual constitution of bodies.

FIG. 357.—_James Prescott Joule, F.R.S._
]

THE GREATEST DISCOVERY OF THE AGE.

The indulgent reader who may have followed the course of the foregoing pages, will perhaps peruse the title of this article with some little bewilderment. His attention has been drawn to one after another of a series of remarkable and important discoveries, and he will naturally wonder what can be the discovery which is greater than any of these. Now, a discovery is great in proportion to the extent and importance of the results that flow from it. These results may be immediate and practical, as in the case of vaccination; or they may be scientific and intellectual, as in Newton’s discovery of the identity of the force which draws a stone to the ground with that which holds the planets in their orbits. Such discoveries as most enlarge our knowledge of the world in which we live, by embracing in simple laws a vast field of phenomena, are precisely those which are most prolific in useful applications. If we admit, as we must, the truth of Bacon’s aphorism, which declares that “Man, as the minister and interpreter of nature, is limited in act and understanding by his observation of the order of nature; neither his understanding nor his power extends farther,”[19] then it would be easy to show that the discovery of which we have to treat, more than any other, must be of immense practical service to mankind in every one of the ways in which a knowledge of the order of nature can be of use, viz.:—“First, In showing in how to avoid attempting impossibilities. Second, In securing us from important mistakes in attempting what is, in itself, possible, by means either inadequate or actually opposed to the end in view. Third, In enabling us to accomplish our ends in the easiest, shortest, most economical, and most effectual manner. Fourth, In inducing us to attempt, and enabling us to accomplish, objects which, but for such knowledge, we should never have thought of undertaking.”[20]

Footnote 19:

“Homo naturæ minister et interpres, tantum facit et intelligit quantum
de naturæ ordine re vel mente observaverit: nec amplius scit aut
potest.”—_Novum Organum, Aphor._ I.

Footnote 20:

Sir J. Herschel.

A great principle, like that which we are about to explain to the reader, is too vast in its bearings for its discovery and elaboration to have been the work of an individual. This truth, and indeed the whole of our knowledge, is but the result of the development and growth of pre-existing knowledge. In fact, every discovery, however brilliant—every invention, however ingenious, is but the expansion or improvement of an antecedent discovery or invention. In strictness, therefore, it is impossible to say where the first germ of even our newest notions may be found. Our latest philosophy can be shown to be the result of progressive modifications of ideas of remote ages. Hence every great truth, every grand invention, has in reality been the offspring of many minds; but we record as _the_ discoverers and inventors those men who have made the longest strides in the path of progress, and whose genius and labours have overcome obstacles defying ordinary efforts.

The extent of the field which is covered by the principle we have in view is so vast—embracing, as it does, the whole phenomena of the universe—that it will not be possible to do more within our limits than give the reader a general notion of the principle itself. It may be useful to instance a truth which has a similar generality and significance, and which has also acquired the force of an axiom, because it is verified every hour. It is that greatest generalization of chemistry, affirming that in all its transformations _matter is indestructible_, and can no more be destroyed than it can be called into being at will. This truth is so well established, that some philosophers have asserted that an opposite state of things is _inconceivable_. But it was not always known; and there are at the present day untutored minds which not only believe that a substance destroyed by fire is utterly annihilated, but what they find _inconceivable_ is the continued existence of the substance in an invisible form. The candle burns away, its matter vanishes from our view; but if we collect the invisible products of the combustion, we find in them the whole substance of the candle in union with the atmospheric oxygen. We may, in imagination, follow the indestructible atoms of carbon in their migrations, from the atmosphere to the plant, which is eaten by the animal and goes to form its fat, and from the tallow, by combustion, back into the atmosphere again. The notion of the real identity of matter under changing forms has been expressed by our great dramatist in a well-known passage, which is remarkable for its philosophic insight, when we consider the age in which it was written:

HAMLET. To what base uses we may return, Horatio! Why may not
imagination trace the noble dust of Alexander, till he find it
stopping a bung-hole?

HORATIO. ‘Twere to consider too curiously to consider so.

HAMLET. No, faith, not a jot; but to follow him thither with
modesty enough, and likelihood to lead it. As thus: Alexander
died, Alexander was buried, Alexander returneth to dust; the dust
is earth; of earth we make loam; and why of that loam, whereto he
was converted, might they not stop a beer-barrel?

Imperial Cæsar, dead, and turned to clay,
Might stop a hole to keep the wind away;
O, that the earth, which kept the world in awe,
Should patch a wall to expel the winter’s flaw!

Now the greatest discovery of our age is that force, like matter, is indestructible, and that it can no more be created than can matter. The reader may perhaps think the statement that we cannot create force is in contradiction to experience. He will be disposed to ask, What is the steam engine for but to create force? Do we not gain force by the pulley, the lever, the hydraulic press? And are not tremendous forces produced when we explode gunpowder or nitro-glycerine? When the principle with which we are here concerned has been developed and stated in accurate terms, it is hoped the reader will see the real nature of these contrivances. We are, however, aware that it is quite impossible within the limits of a short article to do much more than indicate a region of discovery abounding with results which may be yet unfamiliar to some. Into this, if so minded, they should seek for further guidance, which they will pleasantly find in the pages of Dr. Tyndall’s “Heat considered as a Mode of Motion,” and in a little work by Professor Balfour Stewart, entitled “The Conservation of Energy,” and quite fascinating from the clearness and simplicity of its style. We may continue our humble task of merely illustrating the general nature of this, in reality the most important, subject which we have had occasion to bring under the reader’s notice.

Perhaps the first step should be to point out the fact of the various forces of nature—mechanical action, heat, light, electricity, magnetism, chemical action—being so related that any one can be made to produce all the rest directly or indirectly. Some examples of the conversion of one form of force into another occur in the foregoing pages. Thus, on page 485 an experiment is described in which electricity produces a mechanical action; electricity is also shown, on page 496, to produce heat; on page 491 chemical action; on page 501 magnetism. Then, as instances of the inverse actions, there is on page 488, in the first paragraph on “Electric Induction,” an account of the mode in which mechanical movements may give rise to electricity; and in the experiments in pages 508, 509, and particularly in the account of the Gramme machine, page 511, it is shown how mechanical movements can, through magnetism, produce electricity. The voltaic element, page 491, and the galvanic batteries, are instances of chemical action supplying electricity. On page 518 a striking instance is mentioned of changes in the forms of force. Every lighted candle is a case of chemical action giving rise to light; and interesting examples of the inverse relation are referred to on page 608. On page 168 is represented the conversion of arrested motion into heat and light. We have, indeed, sufficient examples to arrange a series of these conversions of forces in a circle. Thus, chemical action (oxidation in the animal system) supplies muscular power, this sets in motion a Gramme machine, the motion is converted into electricity, the electricity produces the electric light, and light causes chemical action, and with this the cycle is complete. In the steam engine heat is converted into mechanical force, and many cases will present themselves to the reader’s mind in which mechanical actions give rise to heat. The doctrine of a mutual dependence and convertibility among all the forms of force was first definitively taught in England by Mr. (now Justice) Grove, in 1842; and almost simultaneously Dr. Meyer promulgated similar views in Germany. Mr. Grove subsequently embodied his doctrine in a treatise, called “The Correlation of the Physical Forces,” which has seen several editions.

But this teaching included much more than a mere connection between the various forces, for it extended to quantitative relations. It declared that a given amount of one force always produced a definite amount of another, that a certain quantity of heat, for example, would give rise to a certain amount of mechanical action, and that this amount of mechanical action was the _equivalent of the heat_ which produced it, and would in its turn reproduce all that heat. These last doctrines, however, rested on a speculative basis, until Mr. James Prescott Joule, of Manchester, carried out a most patient, laborious, and elaborate experimental investigation of the subject. His labours placed the truth of the numerical equivalence of forces on a foundation which cannot be shaken; and he accomplished for the principle of the indestructibility of force what Lavoisier did for that of the indestructibility of matter—he established it on the incontrovertible basis of accurate and conclusive experiment. His determination of the value of the _mechanical equivalent of heat_ especially is a model of experimental research; and subsequent investigators have, by diversified methods, confirmed the accuracy of his results. A great part of his work consisted in finding what quantity of heat would be produced by a given quantity of _work_.

Before we proceed to give an indication of one of Dr. Joule’s methods of making this determination, we may point out that if a weight be raised a certain height, the work which is done in raising it will be given out by the weight in its descent. If you carry a 1 lb. weight to the top of the London Monument, which is 200 ft. high, you perform 200 units of work. When the weight is at the top, the work is not lost; for let the weight be attached to a cord passing over a pulley, and it will, as it descends, draw up to the top another 1 lb. weight.[21] If you drop the weight so that it falls freely, it descends with a continually increasing velocity, strikes the pavement, and comes to rest. Still your work is not lost. The collision of the weight and the pavement develops _heat_, just as in the case of the experiment depicted on page 168, but to a less degree—the increase of temperature might not be sensible to the touch, but could be recognized by delicate instruments. Your work, then, has now changed into the form of heat—the weight and the pavement are hotter than before. This heat is carried off by contiguous substances. But still your work is not lost, for it has made the earth warmer. The heat, however, soon flows away by radiation from the earth, and is diffused into space. The final result of your work is, then, that a certain _measurable_ quantity of heat has been sent off into space. Is your work now finally lost? Not so: in reality, it is only diffused throughout the universe in the form of radiant heat of low intensity. Yet it is lost for ever for useful purposes; for from this final form of diffused heat there is no known or conceivable process by which heat can be gathered up again.

Footnote 21:

See Note B, at the end.

Dr. Joule arranged paddles of brass or iron, so that they could turn freely in a circular box containing water or quicksilver. From the sides of the box partitions projected inwards, which contained openings that permitted the divided arms of the paddle to pass, and preventing the liquid from moving _en masse_, thus caused a churning action when the paddle was turned. Now, every one who has worked a rotatory churn knows that a considerable resistance is offered to this action; but every one does not know that under these circumstances the liquid becomes warmer. It was Dr. Joule’s object to discover how much the temperature of his liquid was raised by a measured quantity of work. He used very delicate thermometers, and had to take a number of precautions which need not here be described; and he obtained the definite quantity of work by the descent of a known weight through a known distance, a cord attached to the weight being wound on a drum, which communicated motion to the paddle. The experiments were conducted with varying circumstances, to avoid chances of error, and were repeated very many times until uniform and consistent indications were always obtained. The result of the experiments showed that 772 units of work (foot-pounds) furnished heat which would raise the temperature of 1 lb. of water from 32° to 33° F., which is the unit of heat. This number, 772, is a constant of the greatest importance in scientific and practical calculations, and is called “_the mechanical equivalent of heat_.” The amount of _work_ it represents is sometimes called a “Joule,” and is always represented in algebraical formulæ by “J.” Mr. Joule’s first paper appeared in 1843, and soon afterwards various branches of the subject of “The Equivalence and Persistence of Forces” were taken up by a number of able men, who have advanced its principles along various lines of inquiry. Among the most noted contributors to this question we find the names of Sir William Thomson, Helmholtz, James Thomson, Rankin, Clausius, Tait, Andrews, and Maxwell.

In the steam engine the case is the inverse of that presented by the above-named experiment of Dr. Joule’s. Here we have heat producing work. Now, the quantity of steam which enters the cylinder of a steam engine may be found, and the temperature of the steam can be determined, and from these the amount of _heat_ which passes into the cylinder per minute, say, can be calculated. A large portion of this heat is, in an ordinary engine, yielded up to the condensing water, and another part is lost by conduction and radiation from the cylinder, condenser, pipes, &c. But both these quantities can be estimated. When the amount is compared with that entering the cylinder in the steam, a difference is always found, which leaves a quantity of heat unaccounted for. When this quantity is compared with the _work_ done by the engine in the same interval (which work can be measured as described on page 10), it is always found that for every 772 units of work a unit of heat has disappeared from the cylinder. The numerical relation between work and heat which is established in these two cases has been tested in many quite different ways; and, within the limits of experimental errors, always with the same numerical result. But equally definite quantitative relations are known to exist among all the other forms of force; and the manner in which these are convertible into each other has already been indicated, although want of space prevents full illustration of this part of the subject. It may, however, be seen that each form of force can be mediately or immediately converted into mechanical effect, hence each is expressible in terms of work. That is to say, we can assign to a unit of electricity, for example, a number expressing the work which it would do if entirely converted into work; and the same number also expresses the work which would be required to produce the unit of electricity. An ounce of hydrogen in combining with 8 oz. of oxygen produces a certain measurable quantity of heat. If that heat, say = H, were all converted into work, we now know that the work would = HJ. Hence we can express a definite chemical action in terms of _work_. The same is generally true of all physical forces, though in some cases, such as light, vital action, &c., the quantitative relations have not yet been definitely determined.

Since, then, all the forces with which we are acquainted are expressible (though the exact relations of some have yet to be discovered) in terms of work, it is found of great advantage to consider the power of doing work as the common measure of doing all these. Thus, if we define _energy_ as that which does, or that which is capable of doing, work, we have a term extremely convenient in the description of some aspects of our subject. Thus we can now speak of the _energies of nature_, instead of the _forces_. And all forces, active or passive, may be summed up in one word—_energy_. And, further, the great discovery of the conservation of forces under definite equivalents, may be summed up very briefly in this statement—THE AMOUNT OF ENERGY IN THE UNIVERSE IS CONSTANT. To make this statement clear requires that a distinction between two forms of every kind of energy be pointed out. To recur to the example before imagined: if you carry the 1 lb. weight up the Monument, and deposit it on the ledge at the top, it might lie there for a thousand years before it was made to give back the work you had performed upon it. That work has been, in a manner, _stored up_ by the _position_ you have given to your weight. Now, in taking up the weight, you expended energy—you really performed work: that is an instance of energy in operation, and may be termed “actual energy.” In what form does the energy exist during the thousand years we may suppose your weight to lie at the top of the Monument? It is ready to yield up your work again at any moment it is permitted to descend, and it possesses therefore during the whole period a _potential energy_ equal in amount to the _actual energy_ you bestowed upon it. A similar distinction between actual and potential energy exists with regard to every form of force. If by any means you separate an atom of carbon from an atom of oxygen, you exert actual energy. The process is analogous to carrying up the weight. The atoms when separated possess _potential_ energy,—they can rush together again, like the weight to the earth, and in doing so will give out the work which was expended on their separation. A parallel illustration might be drawn from electrical force.

A typical example of the storing up of energy is furnished by a crossbow. The moment a man begins to bend the bow he is doing work, because he pulls the string in opposition to the bow’s resistance to a change in its form; and it is plain that the amount of energy thus expended is measurable. Suppose, now, the bow has been bent and the string caught in the notch, from which it is released by drawing the trigger when the discharge of the bow is desired. The bow may be retained for an indefinite period in the bent condition, and in this state it possesses, in the form of _potential energy_, all the work which has been expended in bending it, and which it will, in fact, give out, in some way or other, whenever the trigger is drawn. To fix our ideas, let us suppose that to draw the string over the notch required a pull of 50 lbs. over a space of 6 in.; that is equivalent to 50 × ½ = 25 units of work. Now let the bow be used to shoot an arrow weighing ¼ lb. vertically upwards. The height in feet to which the arrow will rise multiplied into its weight in pounds will be the work done upon it by the bow. Now, we say that experiment proves that in the case supposed the arrow would rise just 100 ft., so that the work done _by_ the bow (¼ × 100 = 25) would be precisely that done _upon it_. For the sake of simplicity, we keep this illustration free from the mention of interfering causes, which have to be considered and allowed for when the matter is put to the real test of quantitative experiment. The instance of the crossbow brings into notice a highly instructive circumstance, which is this: the bow, which it may have taken the strength of a Hercules to bend, will shoot its bolt by the mere touch of a child on the trigger. In the same way, when a man fires a gun, he merely permits the _potential_ energy contained in the charge to convert itself into _actual_, or _kinetic_, energy. The real source of the energy, in the case of the child discharging the crossbow, is the muscular power of the man who drew it; the real source of the energy in exploding gunpowder is the separation of carbon atoms from oxygen atoms, and that has been done by the sun’s rays, as truly as the string was pulled away from the bow by muscular power. If we turn our attention to nitro-glycerine or to nitro-cellulose, we can, by following the chemical actions giving rise to these substances, in like manner trace their energies to our great luminary. The unstable union by which oxygen and nitrogen atoms are locked up in the solid and liquid forms of nitro-cellulose and nitro-glycerine is also the work of the sun; for nitrogen acids, or rather nitrates, are produced naturally under certain electrical and other conditions of the atmosphere, which are due, directly or indirectly, to the sun’s action; and they cannot be formed artificially, except by imitating the natural conditions, as by passing electric sparks through air, &c.

It will now be understood, as regards the wonderful relations between animal and vegetable life, which have already been alluded to more than once, how the sun, by expending actual energy, separates atoms of carbon from atoms of oxygen in the leaves of plants, and confers upon these a position of advantage, _i.e._, potential energy; and how animals, absorbing the separated carbon in the form of food, and inhaling the separated oxygen in the air they breathe, cause the conversion of the potential into actual energy, which appears in the heat, movements, and vital functions of the animal body. In coal we have the energy which plants absorbed from the sun ages ago, stored up in a potential form. The carbon atoms are ready to rush into union with oxygen atoms, and convert their energy of position into the energies developed by chemical action, viz., heat, light, &c. Energy is thus constantly shifting its form from actual to potential, and _vice versâ_, and exhibiting itself under the various transformations of force, as when sun-force changes to chemical action, chemical action to heat, heat to electricity, &c. Energy is, indeed, the real modern PROTEUS—constantly assuming different shapes, difficult to grasp if not held in fetters; now taking on the form of a lion, now of a flame of fire, a whirlwind, a rushing stream. As sober, literal matter of fact we catch glimpses of energy under these very forms.

The greatest discovery of the age has, as already indicated, immediate and important practical bearings. The amount of thought which, even in the present day, is devoted by unscientific mechanics to the old problem of perpetual motion is far greater than is generally supposed. The principle of the conservation of energy shows that this is an impossibility; that the inventor who seeks to create force might just as well try to create matter; that the production of a perpetually moving self-sustaining machine is as far removed from human power as the bringing into existence of a new planet. In force, as in matter, the law is inexorable—_ex nihilo nihil fit_. Again, knowing the definite amount of energy obtainable from the combustion of a pound of coal, we can compare the amount we actually procure from it in our steam engines with this theoretical quantity as the limit towards which our improvements should bring us continually nearer, but which we can never exceed, or, indeed, even reach. The schemers of perpetual motion are not the only class of speculators who pursue objects which are incompatible with our principle. There are many who seek to accomplish desirable ends by inadequate means: who, for example, are aiming perhaps to accomplish the reduction of ores by a quantity of fuel less than that mechanically equivalent to the work, or who conceive that by adding to coal some substance which itself is unchanged, an indefinitely greater amount of heat may be liberated by the combustion.

Enough has been said to show that the energies of animal life can be traced to the sun as their source. The sun builds up the plant, separating oxygen from carbon. The animal—directly or mediately by devouring other animals—takes the carbonaceous matter of the plant, and reunites it with oxygen. In the plant the sun winds up the spring which gives life to the animal mechanism; for the winding-up of a spring and the separation of the atoms having chemical affinities are alike instances of supplying potential energy. In the animal there is a running-down of the potential into actual energy. It is plain also that of the total energy radiated from the sun in every direction, the earth receives but a very small part (1/2300000000). By far the larger part is diffused into space, where, for all such purposes as those with which we are concerned, it is lost. The heat which the sun sends out in a year is calculated to be equal to that which would be produced by the combustion of a layer of coal 17 miles thick over the whole surface of the luminary. Is the sun, then, a flaming fire? By no means. Combustion is not possible at its temperature; and as we know the substances which enter into its composition are the same as those we find in the earth, we know that the chemical energies of such substances could not supply the sun’s expenditure. Passing over as unsatisfactory an explanation which might occur to some minds—namely, that the sun was created hot at the beginning, and has so continued—there are two theories which attempt to account for the sun’s heat. One is that of Meyer, who supposes the heat is due to the continual impact of meteorites drawn to the sun by its gravity; and the other is that of Helmholtz, who attributes the heat to the continual condensation of the substance of the sun. Helmholtz calculates that a shrinking of the sun’s diameter by only 1/10000th of its present amount, would supply heat to last for two thousand years; while the condensation of the substance of the sun to the density of the earth would cover the sun’s expenditure for 17,000,000 of years. There is great probability that both theories may be correct, and that the cause of the sun’s heat may be considered as due in general terms to aggregation of matter, by which the original potential energy of position is converted into the actual energy of heat and light. Now, however immense may be our planetary system, the sun being continually throwing off this energy into space, there must come a time when the supplies of meteorites will fail, and when the great globe of the sun will have shrunk to its smallest dimensions. We see, then, that heat and light are produced by the aggregation of matter; the heat and light are radiated into space; the small fraction intercepted by our globe is the source of almost every movement—the original stuff, so to speak, out of which all terrestrial forces are made. The sun produces the winds, the thunderstorms, the electric currents of the Aurora, the phenomena of terrestrial magnetism, and is the source of vegetable and animal life. The waves, the rains, the mountain torrents, the flowing rivers, are the work of the sun’s emanations.

In the illustration of the energy expended on raising a weight afterwards dropped, we traced that energy into the final form of heat of a low temperature radiated into space. It would be easy to show that all energy ultimately takes the same form. Now, although it is easy to convert work into heat, there is no conceivable process by which uniformly-diffused heat can again be made to do any kind of work. The case may be compared to water, which in moving down from a higher to a lower level may be made to perform any variety of work. But when all the water has passed down from the higher level to the lower, it can no longer do any work. Whenever work is done by the agency of heat, there is always a passing from a higher temperature to a lower—a transference of heat from a hotter body to a colder. If the condenser of the steam engine had the same temperature as the steam, the machine would not work. Not only do all the energies in operation on the face of the earth continually run down into the form of radiant heat sent off by the earth into space; but our sun’s energy, and that of the suns of other systems, are also continually passing off into space; and the final effect must be a uniform diffusion of heat in a universe in which none of the varied forms of energy we now behold in operation will be possible, because all will have run down to the same dead level of uniformly-diffused heat. This startling corollary from the principle of the conservation of energy has been worked out by Sir W. Thomson under the title of “The Dissipation of Energy.” It leads us to contemplate a state of things in which all light and life will have passed away from the universe—a condition which the poet’s terrible dream of darkness, “which was not all a dream,” seems to shadow forth—

“The bright sun was extinguished, and the stars
Did wander darkling in the eternal space,
Rayless and pathless; and the icy earth
Swung blind and blackening in the moonless air.

* * * * *

The world was void,
The populous and the powerful was a lump,
Seasonless, herbless, treeless, manless, lifeless—
A lump of death—a chaos of hard clay.
The rivers, lakes, and ocean all stood still,
And nothing stirred within their silent depths.

* * * * *

The waves were dead; the tides were in their grave,
The Moon, their mistress, had expired before;
The winds were withered in the stagnant air,
And the clouds perished; Darkness had no need
Of aid from them—She was the Universe.”

The doctrine of this persistence and dissipation of energy completely harmonizes with the grand speculation termed the “nebular hypothesis,” which regards the universe as having originally consisted of uniformly diffused matter, which, being endowed with the power of gravitation, aggregated round certain centres. This process is still going on; and, according to modern speculations, light and life and motion are but manifestations of this primæval potential energy being converted into actual energy, and degrading ultimately into the form of universally-diffused heat. To quote the closing sentences of the eloquent passage in which Professor Tyndall concludes the work mentioned above, “To nature nothing can be added, from nature nothing can be taken away; the sum of her energies is constant, and the utmost man can do in the pursuit of physical truth, or in the applications of physical knowledge, is to shift the constituents of the never-varying total. The law of conservation rigidly excludes both creation and annihilation. Waves may change to ripples, and ripples to waves; magnitude may be substituted for number, and number for magnitude; asteroids may aggregate to suns, suns may resolve themselves into floræ and faunæ, and floræ and faunæ melt in air: the flux of power is eternally the same. It rolls in music through the ages, and all terrestrial energy—the manifestations of life as well as the display of phenomena—are but the modulations of its rhythm.”

The discoveries to which we have here endeavoured to attract the reader’s attention thus give rise to conceptions of the utmost grandeur and interest. We see that the sum of Nature’s energies is constant; that all the manifestations of force are but the transference of power from one position to another. And we have recognized the material source of all our terrestrial energies in the sun. Two theories have already been mentioned by which it is sought to account for the sun’s heat—the meteoric theory of Meyer and Thomson, and the shrinkage theory of Helmholtz. These both assume gravitation as the primal force from which the supply of heat and other energies must be drawn, and they assume also that the laws of radiation and of the degradation of temperature in the transformation of heat into other forces, as we find them operating at the earth’s surface, are equally in action in every region of space. Hence is deduced that conception of the final state of the universe as one of merely equally diffused temperature admitting of no further transformation. This speculation presents the _universe_ in the aspect of a clock, now indeed going, but when once run down, incapable of ever being again wound up. There seems in this view a want of symmetry, so to speak; we miss the feeling of harmonious _rhythm_ to which Tyndall refers. There is, however, another cosmic theory, well supported by accumulating facts, which assigns to gravitation a less important part in the production of solar heat and in the evolution of worlds, and it is one which supplies also a basis for the explanation of such phenomena as aerolites, comets, variable stars, the inclination of planets’ axes to their orbits, the proper motion of our sun, and that of the so called fixed stars, of all of which the nebular hypothesis fails to give any account; while, on the other hand, the _impact theory_, as it has been named, includes the other, and goes beyond it. The reader who desires to pursue this subject may be referred to Croll’s book on Stellar Evolution.

In the last few paragraphs we have been dealing with speculations as much as with discoveries. But indeed the former are the offspring of the latter, as certainly as one invention becomes the parent of others. The human mind never rests contented with the knowledge and mastery of nature actually gained, but ever seeks to pass beyond and attain still greater power. The volume we are now bringing to a close has given but brief and imperfect indications of specimens, taken here and there, of what has been done during the short period of one century. We may draw an augury for the future of man’s dominion from the powers his Promethean spirit has already grasped:

“The lightning is his slave; heaven’s utmost deep
Gives up her stars, and like a flock of sheep
They pass before his eye, are numbered, and roll on!
The tempest is his steed, he strides the air;
And the abyss shouts from her depth laid bare,
“Heaven, hast thou secrets? Man unveils me; I have none.”

NOTES A AND B.

_Note A_—_Continuation of Table on page 755, showing the quantity of
Coals raised annually in Great Britain._

Year. Coal raised in Tons.
1874 126,590,108
1875 133,306,458
1876 134,125,166
1877 134,179,968
1878 132,612,063
1879 133,720,393
1880 146,969,409
1881 154,184,300
1882 156,499,977
1883 163,737,327
1884 160,757,779
1885 159,351,418
1886 157,518,482
1887 162,121,576
1888 169,935,219
1889 176,916,724
1890 181,614,280
1891 185,479,126
1892 181,786,871
1893 164,325,795
1894 188,277,525

_Note B_—_CONSERVATION OF ENERGY._—_Page 804._

The statement here should have been more explicit, as it has reference to a state of things not to be realised in practice. Like the well-known “first law of motion,” it can neither be demonstrated _à priori_, nor proved by any direct and simple experiment. The first law of motion asserts that a body in motion, not acted on by any external force, will continue to move in a straight line, and with a uniform velocity. Now we cannot place a body in such a position that it will not be acted upon by some external forces; but the more we lessen the effect of external forces, the more nearly is the motion straight and uniform. Similarly in the case supposed, the intention is to show that the weight carried up is in a position to do just as much work as was done upon it. We must suppose several impracticable but conceivable conditions in order to eliminate considerations which do not concern the theoretical question; we must suppose the cord to be weightless and absolutely devoid of rigidity; the pulley to have no mass or inertia, that is to require no force to set it in motion, and to move without any friction; the air to offer no resistance; and the force of gravity to be uniform throughout the space. Some approximation to these conditions is practicable, as, for example, the pulley might be the lightest possible, and turn on friction wheels, the cord might be the finest silk thread, and so on. But it is not the influence of these external forces we are considering, but only the energy due to the position of the raised weight. Assuming, therefore, the disturbing conditions absolutely eliminated, it is not difficult to see that no downward force or pressure, however small, could be applied for ever so short a time, to the upper weight without setting the system in motion. The motion would be an accelerated one so long as the force was applied, it would become uniform when the force ceased to act; it would have a velocity proportionate to the force. In any case, after a time the descending weight would reach the ground, and for our point of view it is quite immaterial whether the time occupied by the movement were 5 minutes or 5,000 years, for be it observed, time does not enter into the definition of _work_ as it does into that of “horse-power.” Then by pushing the conceived conditions to their limits, we may see that without considering any question of conversion of motion into heat, the raised weight can, in theory at least, give back again the energy spent upon it.

INDEX

A.

Abel, Professor, 746.

Accumulators, 530.

Adhesion of locomotive, 21.

Advantages of present age, 2.

Aerolites, 30.

Air, 734.

Albert Bridge, Saltash, 283.

Alizarine, 797.

“_Alliance_” magneto-electric machine, 520.

Aluminium, 717.
bronze, 719.
reduced cost of, 723.

American Tract Society building, 78.

Ampère’s hypothesis, 750.
rule, 492, 549.

_Amphioxus_, 679.

ANÆSTHETICS, 731.

Anemometer, 656.

Angle, limiting, or critical, 399.

Aniline, 787.
black, 793.
blue, 790.
green, 791.
purple, 788.

Anomalous magnetisation, 538.

_Anthea Cereus_, 678.

Anthracene, 796, 797.

Applegath printing machine, 312.
and Cowper, ditto, 308.

Apps’s anemometer, 656.
induction coil, 506.

AQUARIA, 675.

Arago, 599.

Architecture, use of iron in, 72.

Argand gas burners, 773.
lamps, 595.

Armours, ships’, strengths of, 166.

Armstrong 110–ton gun, 202.

Armstrong’s guns, 192.
hydraulic crane, 333.

Atoms, 733, 743.

Aurora, 504.

Australian gold, 688.

Austrian torpedoes, 229.

“_Automobile_” competition, 23.

Axolotl, 686.

B.

Bacon, Francis, 799.

Balloon, photographic, 628.

Basic process (Gilchrist’s), 66.

Battery, galvanic, 493.

Battery, secondary, 530.

Baxter House experiments, 58.

Bell Rock Lighthouse, 593.

Bells, electro-magnetic, 554.

Benzol, 783.

Bessemer, 26, 56.
Channel steamer, 142.
converter, 63.
iron, 62.
process, 64.
steel, 56–67.

BIG WHEELS, 81.

Bitter Lakes, 261.

BLANCHARD LATHE, THE, 86.

Blast furnace, 40.

Blind spot in eye, 460.

Blister steel, 54.

Blood spectra, 431.

Boilers of steam engines, 13.

Boring for coals, 361.

Bourdon’s pressure gauge, 12.

Bourseul, M., 582.

Box girders, 280.

Breakwater, 258.

Breakwaters for Suez Canal, 258.

BREECH-LOADING RIFLES, 182.

Brewster, Sir D., 405, 420, 470, 474.

Bridge, projected Channel, 296.

Bridgewater Canal, 250, 266.

BRIGHTON AQUARIUM, 682.

Britannia Bridge, 280.
raising tubes, 336.

British Aluminium Co., 723.

British navy in 1894, 167.

BROOKLYN BRIDGE, 303.

“Brown Bess,” 178.

Browning’s micro-spectroscopes, 434.
spectroscope, 422, 432.

Brunel, 283.

Brunswick rifle, 180.

Brush dynamo, 522.

Bullet, Greener’s expanding, 182.
Lebel, 188.
Minié, 180.

Bullets, machinery for making, 330.

Bunsen and Kirchhoff, 422.
and Roscoe, 720.

Bunsen’s battery, 496.
burner, 421.

Bye-products in gas making, 772.

C.

Cable railways, 126.

Cæsium, 426.

Caissons for Forth Bridge, 293.

_Calais-Douvres_, steamship, 141.

Caledonian Canal, 250.

Calico printing machines, 321.

California, discovery of gold in, 688.

Camera, 613.

Canal, Caledonian, 250.
Manchester Ship, 262.
Nicaragua, 274.
North Sea, 271.
Panama, 272.
Suez, 251.

CANTILEVER BRIDGES, 291.

“Cape Horn,” 120.

_Captain_, H.M.S., 141.

Carbon transmitter, 590.

Carbonic oxide, 44, 48.

Carbons for arc lights, 527.

Carcel lamp, 597.

Carpenter, Dr. W. B., 462.

Carriages, railway, 111.
for rock drills, 358.

Carriers in pneumatic tubes, 344.

Cars, Pullman, 112.

_Castalia_, steamship, 139.

Cast-iron, composition of, 43.

Cast steel, 54.

Catoptric lighthouse apparatus, 599.

CAUSE OF LIGHT AND COLOUR, 408.

CELESTIAL CHEMISTRY AND PHYSICS, 436.

Celluloid, 622.

Central Telegraph Office, London, 574.

Centres of gravity and buoyancy, 149.

Centrifugal force, 107.

Chains, 330.

Chain-testing machine, 329.

Channel Bridge (projected), 296.
steamers, 142.

CHANNEL TUNNEL, 364.

Chassepot rifle, 182.

Chemical action of light, 608.
equations, 734.
nomenclature, 782.
symbols, 733.
work of electricity, 497.

Chloroform, 608.

Chromatic aberration of eye, 462.

Chromo-lithography, 638.

Chronograph}

Chronoscope} electric, 656.

Cincinnati Suspension Bridge, 287.

_City of Rome_, steamship, 139.

Clark’s hydraulic lift graving dock, 331.

Clarke’s magneto-electric machine, 509.

Clay process, stereotyping by, 633.

Clerk Maxwell’s theory of light, 541.

“Clermont,” the, 147.

Clifton Suspension Bridge, near Bristol, 285.
Niagara, 287.

COAL, 751.

Coal in Kent, 371.

COAL-GAS, 764.

COAL-TAR COLOURS, 781.

Code, telegraphic, of American War Department, 528.
Morse’s, 560.
Wheatstone’s dot, 565.

Cold-short iron, 62.

Colesberg, 703.

Collodion process, 618.

Colour printing, 639.

Colours not in the objects, 413.
photography of, 628.

Comets, spectra of, 444.

Composition rollers, 406.

Condie’s steam-hammer, 28.

Copying principle, 86.

Cordite, 748.

Corona, 438.

Cort’s puddling furnace, 45.

Couple, mechanical, 149.

Cramp gauge, 129.

Croll, on Stellar Evolution, 810.

Crookes, 507.

Crystal Palace, an example of use of iron in architecture, 72.

Crystal Palace, 72.
AQUARIUM, 677.

Crystalline lens, 455.

Cup and cone, 49.

Current, electric, 492.
induced, 502.
measurement of, 536.

Currents in submarine cables, 579.

D.

Daguerre, 609.

Daguerreotype, 610.

Daimler motor, 24.

Dallmeyer, 617.

Daniell’s battery, 495.

De Beers Mines, 707.

Delphi, oracle at, 739.

Dial telegraphs, 566.

Diamond cutting, 700.

Diamond, qualities of the, 698.
rock drill, 359.

Diamondiferous, 703.

Diamonds, 696.
use of, 701.

Dioptric lighthouse apparatus, 600.

Discoveries, progressive, 802.

Dissipation of energy, 808.

Distinct vision, 458.

D lines of sodium spectrum, 425, 441.

Dolls, talking, 674.

Domestic consumption of coal, 755, 756.

DOUBLE REFRACTION AND POLARIZATION, 399.

Dredges, Suez Canal, 255.

Drilling machine, 90.

Dry digging, 702.

Duboscq’s electric lamp, 497.

Du Moncel, 590.

DYNAMICAL ELECTRICITY, 490.

Dynamo, Siemens’, 522.
Brush, 522.

E.

Earl’s Court, Great Wheel at, 83.

Earth’s circuit, 574.

Ebonite, 728.

Eccentric, 9.

Eclipse of sun, 438.

Eddystone lighthouse, 594.

Edison, 669, 670, 674.

Edison’s kinetoscope, 478.

Eiffel Tower, the, 72.

ELECTRIC LIGHTING AND ELECTRIC POWER, 519.

Electric current, 790.
furnace, 722.

ELECTRIC INDUCTION, 488.
launch, 534.
light, cost of, 43.

Electric light in lighthouses, 515.
telegraph, 598.
torpedo, 547.
tramway, 532.
welding, 537.

ELECTRICITY, 481.

ELECTRICITY, THE NEW, 538.

Electrode, 497.

Electro-magnet, 500.

Electromotive force, 494.

Electro-plating, 499, 518.

Electrotyping, 634.

Elementary bodies, 716.

ELEMENTARY PHENOMENA OF MAGNETISM AND ELECTRICITY, 483.

Elswick 4·7–in. gun, 206.
guns, 194.

Energy, 806.

Ether, 735.
the luminiferous, 408.

Exhaustion of coal, 755, 756, 757.

Expansive working of steam, 8, 17.

Explosion by concussion, 745.
of locomotive, 21.
of torpedoes, 229.

EXPLOSIVES, 225, 740.
different effects of, 748.
names and classes of, 750.

EYE, THE, 451.
dimensions of some parts of, 462.

Eye not optically perfect, 462.

Eyeballs, muscles of, 461.

F.

Fairbairn, Sir W., 280.

Faraday, 506, 508, 735.
ventilating gas-burner, 773.

Faure’s accumulator, 530.

Fellahs, 255.

Ferris wheel, Chicago, 81.

Field telegraphs, 555.

FIRE-ARMS, 169.

Fish-plates, 105.

Fizeau, 386.

Floating matter in air, 383.

Fluids, electric, 487.

Fly-wheels, 7.

Force, conservation of, 804.
electromotive, 494.

FORTH BRIDGE, THE, 311.

Foucault, 387.

Fovea centralis, 456, 457.

Fraser-Woolwich guns, 195.

Fraunhofer’s lines, 420, 436.

Fresnel’s mirrors, 409.
measurement of velocity of light, 600.

Fribourg Suspension Bridge, 286.

Froment’s dial telegraph, 567.

Furnace, electric, 322.

G.

Galvanic batteries, 493, 494.

Galvanometer, 493.
mirror, 570.

Gas engine, 25.
governor, 769.
holder, 766.
making apparatus, 765.
meters, 775.
pressure, 769.
retorts, 766.

Gases of blast furnace, 49.

Gatling battery gun, or mitrailleur, 219.

Gauge, broad and narrow, 106.
Bourdon’s pressure, 12.

Geissler’s tubes, 505.

Ghost, Pepper’s, 392.

Giffard’s injector, 11.

GIRDER BRIDGES, 280.

Glass, strains in, 407.

_Glatton_, H. M. S., 161.

Glynde, electric railway, 534.

GOLD, 686.

GOLD AND DIAMONDS, 687.

Gold-mining operations, 690.

Goodyear, Mr., 727.

Governor of steam engines, 6.

Gower Street Station, 114.

Gramme magneto-electric machine, the, 511.

Graphophone, 672.

Graphotype, 644.

Gray, 590.

GREAT BROOKLYN BRIDGE, 303.

_Great Eastern_, 133, 152, 330, 465, 578.

GREATEST DISCOVERY OF THE AGE, 801.

Greener’s expanding bullet, 182.

Grove, Sir W. R., 804.

Grove’s battery, 495.

Gun, 32–pounder, 191.
68–pounder, 192.
35–ton, 201.
81–ton, 201.
100–ton, 201.
110–ton, 202.
Elswick 4·7–in., 206.
Maxim, 225.
Moncrieff, 208.
Nordenfelt, 223.

Gun-cotton, 747.
torpedoes, 233.

Gunpowder, 734.

Guns, Armstrong’s, 192.
Elswick, 194.
Fraser-Woolwich, 195.
Krupp’s, 214.
quick-firing, 206.
submarine, 240.

GUTTA-PERCHA, 728.

H.

Half-tone process, 629.

Hancock, Mr. Charles, 729.
Mr. Thomas, 725.

Harvey’s torpedoes, 234.

Heat produced by electric current, 502.

Heat spectrum, 613.

Heating by gas, 776.

Helmholtz, 462, 464, 472, 474.

Henry, on Leyden jar discharge, 538.

_Hercules_, H.M.S., 150.

Hertz, Professor, 541.

Hippocampus, 664.

Hoe’s printing machines, 316, 318.

Holmes’ magneto-electric machine, 520.

Holophotal light, 604.

Holyhead and Kingston steamers, 136.

Horseless carriages (_Automobiles_), 23.

Horse-power, 10.

Hot-blast, 48.

Hotchkiss quick-firing guns, 208.

Hough’s metereograph, 654.

Howitzers, 213.

Hudson River steam navigation, 147.

Hughes’ printing telegraph, 560.
microphone, 590.

HYDRAULIC POWER, 324.

I.

Iceland spar, 399.

Illuminating power of gas, 774.

Illusion by movement of eye, 475.
by persistence of vision, 476.
stage, 290.

Images formed by lenses, 399, 616.

Impact theory of Stellar Evolution, 718.

Incandescent electric light, 528.

Incandescent gas-burners, 777.

INCLINED RAILWAYS, 125.

_Inconstant_, H.M.S., 152.

INDIA-RUBBER, 724.

INDIA-RUBBER AND GUTTA-PERCHA, 724.

Indicator, 9.

INDUCED CURRENTS, 502.

Induction coils, 503.

Injector, Giffard’s, 11.

Instantaneous photography, 623.