Chapter VII: Introduction (6)

The bare enumeration of Rumford's published papers would occupy considerable space, but many of them have more to do with philanthropy and domestic economy than with physics. We have seen that, when guest of Lord George Germaine, he was engaged in experiments on gunpowder. The experiments were made in the usual manner by firing bullets into a ballistic pendulum, and recording the swing of the pendulum. Thompson suggested a modification of the ballistic pendulum, attaching the gun-barrel to the pendulum, and observing the recoil, and making allowance for the recoil due to the discharge from the gun of the products of combustion of the powder, the excess enabled the velocity of the bullet to be calculated. Afterwards he made experiments on the maximum pressure produced by the explosion of powder, and pointed out that the value of powder in ordnance does not depend simply on the whole amount of gas produced, but also on the rapidity of combustion. While superintending the arsenal at Munich, Rumford exploded small charges of powder in a specially constructed receiver, which was closed by a plug of well-greased leather, and on this was placed a hemisphere of steel pressed down by a 24-pounder brass cannon weighing 8081 pounds. He found that the weight of the gun was lifted by the explosion of quantities of powder varying from twelve to fifteen grains, and hence concluded that, if the products of combustion of the powder were confined to the space actually occupied by the solid powder, the initial pressure would exceed twenty thousand atmospheres. Rumford's calculation of the pressure, based upon the bursting of a barrel, which he had previously constructed, is not satisfactory, inasmuch as he takes no account of the fact that the inner portions of the metal would give way long before the outer layers exerted anything like their maximum tension. When a hollow vessel with thick walls, such as a gun-barrel or shell, is burst by gaseous pressure from within, the inner layers of material are stretched to their breaking tension before they receive much support from the outer layers; a rift is thus made in the interior, into which the gas enters, and the surface on which the gas presses being thus increased, the rift deepens till the fracture is complete. In order to gain the full strength due to the material employed, every portion of that material should be stretched simultaneously to the extent of its maximum safe load. This principle was first practically adopted by Sir W. G. Armstrong, who, by building up the breech of the gun with cylinders shrunk on, and so arranged that the tension increased towards the exterior, availed himself of nearly the whole strength of the metal employed to resist the explosion. Had Rumford's barrel been constructed on this principle, he would have obtained a much more satisfactory result.

These investigations were followed by a very interesting series of experiments on the conducting power of fluids for heat, and, although he pushed his conclusions further than his experiments warranted, he showed conclusively that convection currents are the principal means by which heat is transferred through the substance of fluids, and described how, when a vessel of water is heated, there is generally an ascending current in the centre, and a descending current all round the periphery. Hence it is only when a liquid expands by increase of temperature that a large mass can be readily heated from below. Water below 39 deg. Fahr. contracts when heated. Rumford, in his paper, enlarges on the bearing of this fact on the economy of the universe, and the following extracts afford a good specimen of his style, and justify some of the statements made by Cuvier in his eulogy:--

I feel the danger to which a mortal exposes himself who has the
temerity to undertake to explain the designs of Infinite Wisdom.
The enterprise is adventurous, but it cannot surely be improper.

The wonderful simplicity of the means employed by the Creator of
the world to produce the changes of the seasons, with all the
innumerable advantages to the inhabitants of the earth which
flow from them, cannot fail to make a very deep and lasting
impression on every human being whose mind is not degraded and
quite callous to every ingenuous and noble sentiment; but the
further we pursue our inquiries respecting the constitution of
the universe, and the more attentively we examine the effects
produced by the various modifications of the active powers which
we perceive, the more we shall be disposed to admire, adore, and
love that great First Cause which brought all things into
existence.

Though winter and summer, spring and autumn, and all the variety
of the seasons are produced in a manner at the same time the
most simple and the most stupendous (by the inclination of the
axis of the earth to the plane of the ecliptic), yet this
mechanical contrivance alone would not have been sufficient (as
I shall endeavour to show) to produce that gradual change of
temperature in the various climates which we find to exist, and
which doubtless is indispensably necessary to the preservation
of animal and vegetable life....

But in very cold countries the ground is frozen and covered with
snow, and all the lakes and rivers are frozen over in the very
beginning of winter. The cold then first begins to be extreme,
and there appears to be no source of heat left which is
sufficient to moderate it in any sensible degree.

Let us see what must have happened if things had been left to
what might be called their natural course--if the condensation
of water, on being deprived of its heat, had followed the law
which we find obtains in other fluids, and even in water itself
in some cases, namely, when it is mixed with certain bodies.

Had not Providence interfered on this occasion in a manner which
may well be considered _miraculous_, all the fresh water within
the polar circle must inevitably have been frozen to a very
great depth in one winter, and every plant and tree destroyed;
and it is more than probable that the region of eternal frost
would have spread on every side from the poles, and, advancing
towards the equator, would have extended its dreary and solitary
reign over a great part of what are now the most fertile and
most inhabited climates of the world!...

Let us with becoming diffidence and awe endeavour to see what
the means are which have been employed by an almighty and
benevolent God to protect His fair creation.

He then goes on to explain how large bodies of water are prevented from freezing at great depths on account of the expansion which takes place on cooling below 39 deg. Fahr., and the further expansion which occurs on freezing, and mentions that in the Lake of Geneva, at a depth of a thousand feet, M. Pictet found the temperature to be 40 deg. Fahr.

"We cannot sufficiently admire the simplicity of the contrivance by which all this heat is saved. It well deserves to be compared with that by which the seasons are produced; and I must think that every candid inquirer who will begin by divesting himself of all unreasonable prejudice will agree with me in attributing them both TO THE SAME AUTHOR....

"But I must take care not to tire my reader by pursuing these speculations too far. If I have persisted in them, if I have dwelt on them with peculiar satisfaction and complacency, it is because I think them uncommonly interesting, and also because I conceived that they might be of value in this age of _refinement_ and _scepticism_.

"If, among barbarous nations, the _fear of a God_, and the practice of religious duties, tend to soften savage dispositions, and to prepare the mind for all those sweet enjoyments which result from peace, order, industry, and friendly intercourse; a _belief in the existence of a Supreme Intelligence_, who rules and governs the universe with wisdom and goodness, is not less essential to the happiness of those who, by cultivating their mental powers, HAVE LEARNED TO KNOW HOW LITTLE CAN BE KNOWN."

Rumford, in connection with his experiments on the conducting power of liquids, tried the effect of increasing the viscosity of water by the addition of starch, and of impeding its movements by the introduction of eider-down, on the rate of diffusion of heat through it. Hence he explained the inequalities of temperature which may obtain in a mass of thick soup--inequalities which had once caused him to burn his mouth--and, applying the same principles to air, he at once turned his conclusions to practical account in the matter of warm clothing.

After an attempt to determine, if possible, the weight of a definite quantity of heat--an attempt in which very great precautions were taken to exclude disturbing causes, while the balance employed was capable of indicating one-millionth part of the weight of the body weighed--Rumford, finding no sensible effect on the balance, concluded that "if the weight of gold is neither augmented nor lessened by _one-millionth part_, upon being heated from the point of _freezing water_ to that of a _bright red heat_, I think we may very safely conclude that ALL ATTEMPTS TO DISCOVER ANY EFFECT OF HEAT UPON THE APPARENT WEIGHTS OF BODIES WILL BE FRUITLESS." The theoretical investigations of Principal Hicks, based on the vortex theory of matter and the dynamical theory of heat, have recently led him to the conclusion that the attraction of gravitation may depend to some extent on temperature.

A series of very valuable experiments on the radiating powers of different surfaces showed how that power varied with the nature of the surface, and the effect of a coating of lamp-black in increasing the radiating power of a body. In order to determine the effect of radiation in the cooling of bodies, Rumford employed the thermoscope referred to by Cuvier. The following passage is worthy of attention, as the truth it expounds in the last thirteen words appears to have been but very imperfectly recognized many years after it was written:--

"All the heat which a hot body loses when it is exposed in the air to cool is not given off to the air which comes into contact with it, but ... a large proportion of it escapes in rays, which do not heat the transparent air through which they pass, but, like light, generate heat only when and where they are stopped and absorbed."

Rumford then investigated the absorption of heat by different surfaces, and established the law that good radiators are good absorbers; and recommended that vessels in which water is to be heated should be blackened on the outside. In speculating on the use of the colouring matter in the skin of the negro, he shows his fondness for experiment:--

"All I will venture to say on the subject is that, were I called to inhabit a very hot country, nothing should prevent me from making the experiment of blackening my skin, or at least, of wearing a black shirt, in the shade, and especially at night, in order to find out if, by those means, I could contrive to make myself more comfortable."

In his experiments on the conduction of heat, Rumford employed a cylinder with one end immersed in boiling water and the other in melting ice, and determined the temperature at different points in the length of the cylinder. He found the difficulty which has recently been forcibly pointed out by Sir Wm. Thomson, in the article "Heat," in the "Encyclopaedia Britannica," viz. that the circulation of the water was not sufficiently rapid to keep the temperature of the layer in contact with the metal the same as that of the rest of the water; and he also called attention to the arbitrary character of thermometer-scales, and recommended that more attention should be given to the scale of the air thermometer. It was in his visit to Edinburgh, in 1800, that, in company with some of the university professors, the count conducted some experiments in the university laboratory on the apparent radiation of cold. Rumford's views respecting _frigorific rays_ have not been generally accepted, and Prevost's theory of exchanges completely explains the apparent radiation of cold without supposing that cold is anything else than the mere absence of heat.

We must pass over Rumford's papers on the use of steam as a vehicle of heat, on new boilers and stoves for the purpose of economizing fuel, and all the papers bearing on the nutritive value of different foods. The calorimeter with which he determined the amount of heat generated by the combustion, and the latent heat of evaporation, of various bodies has been already alluded to. Of the four volumes of Rumford's works published by the American Academy of Arts and Sciences, the third is taken up entirely with descriptions of fireplaces and of cooking utensils.

Before deciding on the best way to light the military workhouse at Munich, Rumford made a series of experiments on the relative economy of different methods, and for this purpose designed his well-known shadow-photometer. In the final form of this instrument the shadows were thrown on a plate of ground glass covered with paper, forming the back of a small box, from which all extraneous light was excluded. Two rods were placed in front of this screen, and the lights to be compared were so situated that the shadow of one rod thrown by the first light might be just in contact with that of the other rod thrown by the second light. By introducing coloured glasses in front of the lights, Rumford compared the illuminating powers of different sources with respect to light of a particular colour. The complementary tints exhibited by the shadows caused him to devise his theory of the harmony of complementary colours. One result is worthy of mention: it is a conclusion to which public attention has since been called in connection with "duplex" burners. Rumford found that with wax tapers the amount of light emitted per grain of wax consumed diminished with the diminution of the consumption, so that a small taper gave out only one-sixteenth as much light as an ordinary candle for the same consumption of wax. He says:--

"This result can be easily explained if we admit the hypothesis which supposes light to be analogous to sound.... The particles ... were so rapidly cooled ... that they had hardly time to shine one instant before they became too cold to be any longer visible."

An argand lamp, when compared with a lamp having a flat wick, gave more light in the ratio of 100 to 85 for the same consumption of oil.

One of the latest investigations of Rumford was that bearing on the effect of the width of the wheels on the draught of a carriage. To his own carriage, weighing, with its passengers, nearly a ton, he fitted a spring dynamometer by means of a set of pulleys attached to the under-carriage and the splinter-bar. He used three sets of wheels, respectively 1-3/4, 2-1/4, and 4 inches wide, and, introducing weights into the carriage to make up for the difference in the weights of the wheels, he found a very sensible diminution in the tractive force required as the width of the wheels was increased, and in a truly scientific spirit, despising the ridicule cast upon him, he persisted in riding about Paris in a carriage with four-inch tyres.

But the piece of work by which Rumford will be best known to future generations is that described in his paper entitled "An Inquiry concerning the Source of the Heat which is excited by Friction." It was while superintending the boring of cannon in the arsenal at Munich that Rumford was struck with the enormous amount of heat generated by the friction of the boring-bar against the metal. In order to determine whether the heat had come from the chips of metal themselves, he took a quantity of the abraded borings and an equal weight of chips cut from the metal with a fine saw, and, heating them to the temperature of boiling water, he immersed them in equal quantities of water at 59-1/2 deg. Fahr. The change of temperature of the water was the same in both cases, and Rumford found that there was no change which he could discover _in regard to its capacity for heat_ produced in the metal by the action of the borer.

In order to prevent the honeycombing of the castings by the escaping gas, the cannon were cast in a vertical position with the breech at the bottom of the mould and a short cylinder projecting about two feet beyond the muzzle of the gun, so that any imperfections in the casting would appear in this projecting cylinder. It was on one of these pieces of waste metal, while still attached to the gun, that Rumford conducted his experiments. Having turned the cylinder, he cut away the metal in front of the muzzle until the projecting piece was connected with the gun by a narrow cylindrical neck, 2.2 inches in diameter and 3.8 inches long. The external diameter of the cylinder was 7.75 inches, and its length 9.8 inches, and it was bored to a depth of 7.2 inches, the diameter of the bore being 3.7 inches. The cannon was mounted in the boring-lathe, and a blunt borer pressed by a screw against the bottom of the bore with a force equal to the weight of 10,000 pounds. A small transverse hole was made in the cylinder near its base for the introduction of a thermometer. The cylinder weighed 113.13 pounds, and, with the gun, was turned at the rate of thirty-two revolutions per minute by horse-power. To prevent loss of heat, the cylinder was covered with flannel. After thirty minutes' work, the thermometer, when introduced into the cylinder, showed a temperature of 130 deg. Fahr. The loss of heat during the experiment was estimated from observations of the rate of cooling of the cylinder. The weight of metal abraded was 837 grains, while the amount of heat produced was sufficient to raise nearly five pounds of ice-cold water to the boiling point.

To exclude the action of the air, the cylinder was closed by an air-tight piston, but no change was produced in the result. As the air had access to the metal where it was rubbed by the piston, and Rumford thought this might possibly affect the result, a deal box was constructed, with slits at each end closed by sliding shutters, and so arranged that it could be placed with the boring bar passing through one slit and the narrow neck connecting the cylinder with the gun through the other slit, the sliding shutters, with the help of collars of oiled leather, serving to make the box water-tight. The box was then filled with water and the lid placed on. After turning for an hour the temperature was raised from 60 deg. to 107 deg. Fahr., after an hour and a half it was 142 deg. Fahr., at the end of two hours the temperature was 178 deg. Fahr., at two hours and twenty minutes it was 200 deg. Fahr., and at two hours and thirty minutes it ACTUALLY BOILED!

"It would be difficult to describe the surprise and astonishment expressed in the countenances of the bystanders on seeing so large a quantity of cold water heated and actually made to boil without any fire.

"Though there was, in fact, nothing that could justly be considered as surprising in this event, yet I acknowledge fairly that it afforded me a degree of childish pleasure which, were I ambitious of the reputation of a _grave philosopher_, I ought most certainly rather to hide than to discover."

Rumford estimated the "total quantity of ice-cold water which, with the heat actually generated by the friction and accumulated in two hours and thirty minutes, might have been heated 180 degrees, or made to boil" at 26.58 pounds, and the rate of production he considered exceeded that of nine wax candles, each consuming ninety-eight grains of wax per hour, while the work of turning the lathe could easily have been performed by one horse. This was the first rough attempt ever made, so far as we know, to determine the mechanical equivalent of heat.

In his reflections on these experiments, Rumford writes:--

It is hardly necessary to add that anything which any
_insulated_ body or system of bodies can continue to furnish
_without limitation_ cannot possibly be _a material substance_;
and it appears to me to be extremely difficult, if not quite
impossible, to form any distinct idea of anything capable of
being excited and communicated in the manner the heat was
excited and communicated in these experiments, except it be
MOTION.

It has been stated that, if Rumford had dissolved in acid the borings and the sawn strips of metal, the capacity for heat of which he determined, and had shown that the heat developed in the solution was the same in the two cases, his chain of argument would have been absolutely complete. Considering the amount of heat produced in the experiments, there are few minds whose conviction would be strengthened by this experiment, and it is only those who look for faultless logic that will refuse to Rumford the credit of having established the dynamical nature of heat.

Davy afterwards showed that two pieces of ice could be melted by being rubbed against one another in a vacuum, but he does not appear to have made as much as he might of the experiment. Mayer calculated the mechanical equivalent of heat from the heat developed in the compression of air, but he _assumed_, what afterwards was shown by Joule to be nearly true, that the whole of the work done in the compression was converted into heat. It was Joule, however, who first showed that heat and mechanical energy are mutually convertible, so that each may be expressed in terms of the other, a _given_ quantity of heat always corresponding to the _same amount_ of mechanical energy, whatever may be the intermediate stages through which it passes, and that we may therefore define the mechanical equivalent of heat as _the number of units of energy which, when entirely converted into heat, will raise unit mass of water one degree from the freezing point_.

THOMAS YOUNG.

"We here meet with a man altogether beyond the common standard, one in whom natural endowment and sedulous cultivation rivalled each other in the production of a true philosopher; nor do we hesitate to state our belief that, since Newton, Thomas Young stands unrivalled in the annals of British science." Such was the verdict of Principal Forbes on one who may not only be regarded as one of the founders of the undulatory theory of light, but who was among the first to apply the theory of elasticity to the strength of structures, while it is to him that we are indebted in the first instance for all we know of Egyptian hieroglyphics, and for the vast field of antiquarian research which the interpretation of these symbols has opened up.

Thomas Young was the son of Thomas and Sarah Young, and the eldest of ten children. His mother was a niece of the well-known physician, Dr. Richard Brocklesby, and both his father and mother were members of the Society of Friends, in whose principles all their children were very carefully trained. It was to the independence of character thus developed that Dr. Young attributed very much of the success which he afterwards attained. He was born at Milverton, in Somersetshire, on June 13, 1773. For the greater part of the first seven years of his life he lived with his maternal grandfather, Mr. Robert Davis, at Minehead, in Somersetshire. According to his own account, he could read with considerable fluency at the age of _two_, and, under the instructions of his aunt and a village schoolmistress, he had "read the Bible twice through, and also Watts's Hymns," before he attained the age of four. It may with reason be thought that both the schoolmistress and the aunt should have been severely reprimanded, and it is certain that their example is not to be commended; but Young's infantile constitution seems to have been proof against over-pressure, and before he was five years old he could recite the whole of Goldsmith's "Deserted Village," with scarcely a mistake. He commenced learning Latin before he was six, under the guidance of a Nonconformist minister, who also taught him to write. When not quite seven years of age he went to boarding-school, where he remained a year and a half; but he appears to have learned more by independent effort than under the guidance of his master, for privately he "had mastered the last rules of Walkinghame's 'Tutor's Assistant'" before reaching the middle of the book under the master's inspection. After leaving this school, he lived at home for six months, but frequently visited a neighbour who was a land surveyor, and at whose house he amused himself with philosophical instruments and scientific books, especially a "Dictionary of Arts and Sciences." When nearly nine he went to the school of Mr. Thompson, at Compton, in Dorsetshire, where he remained nearly four years, and read several Greek and Latin authors, as well as the elements of natural philosophy--the latter in books lent him by Mr. Jeffrey, the assistant-master. This Mr. Jeffrey appears to have been something of a mechanical genius, and he gave Young lessons in turning, drawing, bookbinding, and the grinding and preparation of colours. Before leaving this school, at the age of thirteen, Young had read six chapters of the Hebrew Bible.

During the school holidays the construction of a microscope occupied considerable time, and the reading of "Priestley on Air" turned Young's attention to the subject of chemistry. Having learned a little French, he succeeded, with the help of a schoolfellow, in gaining an elementary knowledge of Italian. After leaving school, he lived at home for some time, and devoted his energies mainly to Hebrew and to turning and telescope-making; but Eastern languages received a share of attention, and by the time he was fourteen he had read most of Sir William Jones's "Persian Grammar." He then went to Youngsbury, in Hertfordshire, and resided at the house of Mr. David Barclay, partly as companion and partly as classical tutor to Mr. Barclay's grandson, Hudson Gurney. This was the beginning of a friendship which lasted for life. Gurney was about a year and a half junior to Young, and for five years the boys studied together, reading the classical works which Young had previously studied at school. Before the end of these five years Young had gained more or less acquaintance with fourteen languages; but his studies were for a time delayed through a serious illness when he was little more than sixteen. To this illness his uncle, Dr. Brocklesby, referred in a letter, of which the following extract is interesting for several reasons:--

Recollect that the least slip (as who can be secure against
error?) would in you, who seem in all things to set yourself
above ordinary humanity, seem more monstrous or reprehensible
than it might be in the generality of mankind. Your prudery
about abstaining from the use of sugar on account of the negro
trade, in any one else would be altogether ridiculous, but as
long as the whole of your mind keeps free from spiritual pride
or too much presumption in your facility of acquiring language,
which is no more than the dross of knowledge, you may be
indulged in such whims, till your mind becomes enlightened with
more reason. My late excellent friend, Mr. Day, the author of
'Sandford and Merton,' abhorred the base traffic in negroes'
lives as much as you can do, and even Mr. Granville Sharp, one
of the earliest writers on the subject, has not done half as
much service in the business as Mr. Day in the above work. And
yet Mr. Day devoured daily as much sugar as I do; for he
reasonably concluded that so great a system as the sugar-culture
in the West Indies, where sixty millions of British property are
employed, could never be affected either way by one or one
hundred in the nation debarring themselves the reasonable use of
it. Reformation must take its rise elsewhere, if ever there is a
general mass of public virtue sufficient to resist such private
interests. Read Locke with care, for he opens the avenues of
knowledge, though he gives too little himself.

With respect to the sugar, no doubt very much may be said on Young's side of the question. It appears, however, that in his early manhood there was a good deal in his conduct which to-day would be regarded as _priggish_, though it was somewhat more in harmony with the spirit of his time.

He left Youngsbury at the age of nineteen, having read, besides his classical authors, the whole of Newton's "Principia" and "Opticks," and the systems of chemistry by Lavoisier and Nicholson, besides works on botany, medicine, mineralogy, and other scientific subjects. One of Young's peculiarities was the extraordinary neatness of his handwriting, and a translation in Greek iambics of Wolsey's farewell to Cromwell, which he sent, written very neatly on vellum, to his uncle, Dr. Brocklesby, attracted the attention of Mr. Burke, Dr. Charles Burney, and other classical scholars, so that when, a few months later, Young went to stay with his uncle in London, and was thrown into contact with some of the chief literary men of the day, he found that his fame as a scholar had preceded him. This neatness of his handwriting and his power of drawing were of great use in his researches on the Egyptian hieroglyphics. He had little faith in natural genius, but believed that anything could be accomplished by persevering application.

"Thou say'st not only skill is gained,
But genius too may be obtained,
By studious imitation."

In the autumn of 1792 Young went to London for the purpose of studying medicine. He lived in lodgings in Westminster, and attended the Hunterian School of Anatomy. A year afterwards he entered St. Bartholomew's Hospital as a medical student. The notes which he took of the lectures were written sometimes in Latin, interspersed with Greek quotations, and not unfrequently with mathematical calculations, which may be assumed to have been made before the lecture commenced. During his school days he had paid some attention to geometrical optics, and had constructed a microscope and telescope. Now his attention was attracted to a far more delicate instrument--the eye itself. Young had learned how a telescope can be "focussed" so as to give clear images of objects more or less distant. Some such power of adjustment must be possessed by the eye, or it could never form distinct images of objects, whether at a distance of a foot or a mile. The apparently fibrous structure of the crystalline lens of the eye had been noticed and described by Leuwenhoeck; and Pemberton, a century before Young took up the subject, had suggested that the fibres were muscles, by the action of which the eye was "accommodated" for near or distant vision. In dissecting the eye of an ox Young thought he had discovered evidence confirmatory of this view, and the paper which he wrote on the subject was not only published in the "Philosophical Transactions," but secured his election as a Fellow of the Royal Society in June, 1794. This paper was important, not simply because it led to Young's election to the Royal Society, but mainly because it was his first published paper on optical subjects. Later on he showed incontestably, by exact measurements, that it is the crystalline lens which changes its form during adjustment; but he was wrong in supposing the fibres of the lens to be muscular. By carefully measuring the distance between the images of two candles formed by reflection from the cornea, he showed that the cornea experienced no change of form. His eyes were very prominent; and turning them so as to look very obliquely, he measured the length of the eye from back to front with a pair of compasses whose points were protected, pressing one point against the cornea, and the other between the back of the eye and the orbit, and showed that, when the eye was focussed for different distances, there was no change in the length of the axis. The crystalline lens was the only resource left whereby the accommodation could be effected. The accommodation is, in fact, brought about by the action of the ciliary muscle. The natural form of the lens is more convex than is consistent with distinct vision, except for very near objects. The tension of the suspensory ligament, which is attached to the front of the lens all round its edge, renders the anterior surface of the lens much less curved than it would naturally be. The ciliary muscle is a ring of muscular fibre attached to the ciliary process close to the circumference of the suspensory ligament. By its contraction it forms a smaller ring, and, diminishing the external diameter, it releases the tension of the suspensory ligament, thus allowing the crystalline lens to bulge out and adapt itself for the diverging rays coming from near objects. It is the exertion of contracting the ciliary muscle that constitutes the effort of which we are conscious when looking at very near objects. It was not, however, till long after the time of Dr. Young that this complicated action was fully made out, though the change of form of the anterior surface of the crystalline lens was discovered by the change in the image of a bright object formed by reflection.

In the spring of 1794 Young took a holiday tour in Cornwall, with Hudson Gurney, visiting on his way the Duke of Richmond, who was drinking the waters at Bath, under the advice of Dr. Brocklesby. In Cornwall, the mining machinery attracted his attention very much more than the natural beauties of the country. Towards the end of the summer he visited the Duke of Richmond at Goodwood, when the duke offered him the appointment of private secretary. He resolved, however, to continue his medical course, one of the reasons which he alleged being his regard for the Society of Friends, whose principles he considered inconsistent with the appointment of Private Secretary to the Master-General of the Ordnance.

The following winter he spent as a medical student at Edinburgh. Here he gave up the costume of the Society of Friends, and in many ways departed from their rules of conduct. He mingled freely with the university, attended the theatre, took lessons in dancing and playing the flute, and generally cultivated the habits of what is technically known as "society." Throughout this change in his life he retained his high moral principles as a guide of conduct, and appears to have acted from a firm conviction of what was right. At the same time, it must be admitted that the breaking down of barriers, however conventional they may be, is an operation attended in most cases by not a little danger. With Young, the progress of his scientific education may have been delayed on account of the new demands on his time; but besides the study of German, Spanish, and Italian, he appears to have read a considerable amount of general literature during his winter session in Edinburgh. The following summer he took a tour on horseback through the Highlands, taking with him his flute, drawing materials, spirits for preserving insects, boards for drying plants, paper and twine for packing up minerals, and a thermometer; but the geological hammer does not then appear to have been regarded as an essential to the equipment of a philosopher. At Aberdeen he stayed for three days, and reported thus on the university:--

Some of the professors are capable of raising a university to
celebrity, especially Copeland and Ogilvie; but the division and
proximity of the two universities (King's College and Marischal
College) is not favourable to the advancement of learning;
besides, the lectures are all, or mostly, given at the same
hour, and the same professor continues to instruct a class for
four years in the different branches. Were the colleges united,
and the internal regulations of the system new modelled, the
cheapness of the place, the number of small bursaries for poor
or distinguished students, and the merit of the instructors,
might make this university a very respectable seminary in some
branches of science. The fee to a professor for a five-months'
session is only a guinea and a half. I was delighted with the
inspection of the rich store of mathematical and philosophical
apparatus belonging to Professor Copeland of Marischal College,
made in his own house, and partly with his own hands, finished
with no less care than elegance; and tending to illustrate every
branch of physics in the course of his lectures, which must be
equally entertaining and instructive.

Before leaving the Highlands, Young visited Gordon Castle, where he stayed two days; and appears to have distinguished himself by the powers of endurance he exhibited in dancing reels. On leaving he writes: "I could almost have wished to break or dislocate a limb by chance, that I might be detained against my will; I do not recollect that I have ever passed my time more agreeably, or with a party that I thought more congenial to my own dispositions: and what would hardly be credited by many grave reasoners on life and manners, that a person who had spent the whole of his earlier years a recluse from the gay world, and a total stranger to all that was passing in the higher ranks of society, should feel himself more at home and more at ease in the most magnificent palace in the country than in the humblest dwelling with those whose birth was most similar to his own. Without enlarging on the duke's good sense and sincerity, the duchess's spirit and powers of conversation, Lady Madeline's liveliness and affability, Louisa's beauty and sweetness, Georgiana's _naivete_ and quickness of parts, young Sandy's good nature, I may say that I was truly sorry to part with every one of them."

Young seems not to have known at this time that it is an essential feature of true gentlefolk to dissipate all sense of constraint or uneasiness from those with whom they are brought into contact and that in this they can be readily distinguished from those who have wealth without breeding. The Duchess of Gordon gave Young an introduction to the Duke of Argyll, so, while travelling through the Western Highlands, he paid a visit to Inverary Castle, and "galloped over" the country with the duke's daughters. Speaking of these ladies, he says, "Lady Charlotte ... is to Lady Augusta what Venus is to Minerva; I suppose she wishes for no more. Both are goddesses."

On his return to the West of England, he visited the Coalbrook Dale Iron Works, when Mr. Reynolds told him "that before the war he had agreed with a man to make a flute a hundred and fifty feet long, and two and a half in diameter, to be blown by a steam-engine and played on by barrels."

On the 7th of the following October Young left London, and after spending six days on the voyage from Yarmouth to Hamburg, he reached Goettingen on the 27th of the same month; two days afterwards he matriculated, and on November 3 he commenced his studies as a member of the university. He continued to take lessons in drawing, dancing, riding, and music, and commenced learning the clavichord. The English students at Goettingen, in order to advance their German conversation, arranged to pay a fine whenever they spoke in English in one another's company. On Sundays it was usual for the professors to give entertainments to the students, though they seldom invited them to dinner or supper. "Indeed, they could not well afford, out of a fee of a louis or two, to give large entertainments; but the absence of the hospitality which prevails rather more in Britain, is compensated by the light in which the students are regarded; they are not the less, but perhaps the more, respected for being students, and indeed, they behave in general like gentlemen, much more so than in some other German universities."

At Goettingen Young attended, in addition to his medical lectures, Spithler's lectures on the History and Constitution of the European States, Heyne on the History of the Ancient Arts, and Lichtenberg's course on Physics. Speaking of Blumenbach's lectures on Natural History, Young says, "He showed us yesterday a laborious treatise, with elegant plates, published in the beginning of this century at Wurzburg, which is a most singular specimen of credulity in affairs of natural history. Dr. Behringen used to torment the young men of a large school by obliging them to go out with him collecting petrifactions; and the young rogues, in revenge, spent a whole winter in counterfeiting specimens, which they buried in a hill which the good man meant to explore, and imposed them upon him for most wonderful _lusus naturae_. It is interesting in a metaphysical point of view to observe how the mind attempts to accommodate itself; in one case, where the boys had made the figure of a plant thick and clumsy, the doctor remarks the difference, and says that Nature seems to have restored to the plant in thickness that which she had taken away from its other dimensions."

On April 30, 1796, Young passed the examination for his medical degree at Goettingen. The examination appears to have been entirely oral. It lasted between four and five hours. There were four examiners seated round a table provided "with cakes, sweetmeats, and wine, which helped to pass the time agreeably." They "were not very severe in exacting accurate answers." The subject he selected for his public discussion was the human voice, and he constructed a universal alphabet consisting of forty-seven letters, of which, however, very little is known. This study of sound laid the foundation, according to his own account, of his subsequent researches in the undulatory theory of light.

The autumn of 1796 Young spent in travelling in Germany; in the following February he returned to England, and was admitted a fellow-commoner of Emmanuel College, Cambridge. It is said that the Master, in introducing Young to the Tutors and other Fellows, said, "I have brought you a pupil qualified to read lectures to his tutors." Young's opinion of Cambridge, as compared with German universities, was favourable to the former; but as he had complained of the want of hospitality at Goettingen, so in Cambridge he complained of the want of social intercourse between the senior members of the university and persons _in statu pupillari_. At that time there was no system of medical education in the university, and the statutes required that six years should elapse between the admission of a medical student and his taking the degree of M.B. Young appears to have attracted comparatively little attention as an undergraduate in college. He did not care to associate with other undergraduates, and had little opportunity of intercourse with the senior members of the university. He was still keeping terms at Cambridge when his uncle, Dr. Brocklesby, died. To Young he left the house in Norfolk Street, Park Lane, with the furniture, books, pictures, and prints, and about L10,000. In the summer of 1798 a slight accident at Cambridge compelled Young to keep to his rooms, and being thus forcibly deprived of his usual round of social intercourse, he returned to his favourite studies in physics. The most important result of this study was the establishment of the principle of interference in sound, which afforded the explanation of the phenomenon of "beats" in music, and which afterwards led up to the discovery of the interference of light--a discovery which Sir John Herschel characterized as "the key to all the more abstruse and puzzling properties of light, and which would alone have sufficed to place its author in the highest rank of scientific immortality, even were his other almost innumerable claims to such a distinction disregarded."

The principle of interference is briefly this: When two waves meet each other, it may happen that their crests coincide; in this case a wave will be formed equal in height (amplitude) to the sum of the heights of the two. At another point the crest of one wave may coincide with the hollow of another, and, as the waves pass, the height of the wave at this point will be the difference of the two heights, and if the waves are equal the point will remain stationary. If a rope be hung from the ceiling of a lofty room, and the lower end receive a jerk from the hand, a wave will travel up the rope, be reflected and reversed at the ceiling, and then descend. If another wave be then sent up, the two will meet, and their passing can be observed. It will then be seen that, if the waves are exactly equal, the point at which they meet will remain at rest during the whole time of transit. If a number of waves in succession be sent up the string, the motions of the hand being properly timed, the string will appear to be divided into a number of vibrating segments separated by stationary points, or nodes. These nodes are simply the points which remain at rest on account of the upward series of waves crossing the series which have been reflected at the top and are travelling downwards. The division of a vibrating string into nodes thus affords a simple example of the principle of interference. When a tuning-fork is vibrating there are certain hyperbolic lines along which the disturbance caused by one prong is exactly neutralized by that due to the other prong. If a large tuning-fork be struck and then held near the ear and slowly turned round, the positions of comparative silence will be readily perceived. If two notes are being sounded side by side, one consisting of two hundred vibrations per second and the other of two hundred and two, then, at any distant point, it is clear that the two sets of waves will arrive in the same condition, or "phase," twice in each second, and twice they will be in opposite conditions, and, if of the same intensity, will exactly destroy one another's effects, thus producing silence. Hence twice in the second there will be silence and twice there will be sound, the waves of which have double the amplitude due to either source, and hence the sound will have four times the intensity of either note by itself. Thus there will be two "beats" per second due to interference. Later on this principle was applied by Young to very many optical phenomena of which it afforded a complete explanation.

Young completed his last term of residence at Cambridge in December, 1799, and in the early part of 1800 he commenced practice as a physician at 48, Welbeck Street. In the following year he accepted the chair of Natural Philosophy in the Royal Institution, which had shortly before been founded, and soon afterwards, in conjunction with Davy, the Professor of Chemistry, he undertook the editing of the journals of the institution. This circumstance has already been alluded to in connection with Count Rumford, the founder of the institution. He lectured at the Royal Institution for two years only, when he resigned the chair in deference to the popular belief that a physician should give his attention wholly to his professional practice, whether he has any or not. This fear lest a scientific reputation should interfere with his success as a physician haunted him for many years, and sometimes prevented his undertaking scientific work, while at other times it led him to publish anonymously the results he obtained. This anonymous publication of scientific papers caused him great trouble afterwards in order to establish his claim to his own discoveries. Many of the articles which he contributed to the supplement to the fourth, fifth, and sixth editions of the "Encyclopaedia Britannica" were anonymous, although the honorarium he received for this work was increased by 25 per cent. when he would allow his name to appear. The practical withdrawal of Young from the scientific world during sixteen years was a great loss to the progress of natural philosophy, while the absence of that suavity of manner when dealing with patients which is so essential to the success of a physician, prevented him from acquiring a valuable private practice. In fact, Young was too much of a philosopher in his behaviour to succeed as a physician; he thought too deeply before giving his opinion on a diagnosis, instead of appearing to know all about the subject before he commenced his examination, and this habit, which is essential to the philosopher, does not inspire confidence in the practitioner. His fondness for society rendered him unwilling to live within the means which his uncle had left him, supplemented by what his scientific work might bring, and it was not until his income had been considerably increased by an appointment under the Admiralty that he was willing to forego the possible increase of practice which might accrue by appearing to devote his whole attention to the subject of medicine. It was this fear of public opinion which caused him, in 1812, to decline the offer of the appointment of Secretary to the Royal Society, of which, in 1802, he accepted the office of Foreign Secretary.

Young's resignation of the chair of Natural Philosophy was, however, not a great loss to the Royal Institution; for the lecture audience there was essentially of a popular character, and Young cannot be considered to have been successful as a popular lecturer. His own early education had been too much derived from private reading for him to have become acquainted with the difficulties experienced by beginners of only average ability, and his lectures, while most valuable to those who already possessed a fair knowledge of the subjects, were ill adapted to the requirements of an unscientific audience. A syllabus of his course of lectures was published by Young in 1802, but it was not till 1807 that the complete course of sixty lectures was published in two quarto volumes. They were republished in 1845 in octavo, with references and notes by Professor Kelland. Among the subjects treated in these lectures are mechanics, including strength of materials, architecture and carpentry, clocks, drawing and modelling; hydrostatics and hydraulics; sound and musical instruments; optics, including vision and the physical nature of light; astronomy; geography; the essential properties of matter; heat; electricity and magnetism; climate, winds, and meteorology generally; vegetation and animal life, and the history of the preceding sciences. The lectures were followed by a most complete bibliography of the whole subject, including works in English, French, German, Italian, and Latin. The following is the syllabus of one lecture, and illustrates the diversity of the subjects dealt with:--

"ON DRAWING, WRITING, AND MEASURING.

"Subjects preliminary to the study of practical mechanics;
instrumental geometry; statics; passive strength; friction;
drawing; outline; pen; pencil; chalks; crayons; Indian ink;
water-colours; body colours; miniature; distemper; fresco; oil;
encaustic paintings; enamel; mosaic work. Writing; materials
for writing; pens; inks; use of coloured inks for denoting
numbers; polygraph; telegraph; geometrical instruments; rulers;
compasses; flexible rulers; squares; triangular compasses;
parallel rulers; Marquois's scales; pantograph; proportional
compasses; sector. Measurement of angles; theodolites;
quadrants; dividing-engine; vernier; levelling; sines of
angles; Gunter's scale; Nicholson's circle; dendrometer;
arithmetical machines; standard measures; quotation from
Laplace; new measures; decimal divisions; length of the
pendulum and of the meridian of the earth; measures of time;
objections; comparison of measures; instruments for measuring;
micrometrical scales; log-lines."

This represents an extensive area to cover in a lecture of one hour.

When Newton, by means of a prism,

"Unravelled all the shining robe of day,"

he showed that sunlight is made up of light varying in tint from red, through orange, yellow, green, and blue, to violet, and that by recombining all these kinds of light, or certain of them selected in an indefinite number of ways, white light could be produced. Subsequently Sir Wm. Herschel showed that rays less refrangible than the red were to be found among the solar radiation; and other rays more refrangible than the violet, but, like the ultra-red rays, incapable of exciting vision, were found by Ritter and Wollaston. In speaking of Newton's experiments, in his thirty-seventh lecture, Young says:--

It is certain that the perfect sensations of yellow and of blue
are produced respectively by mixtures of red and green and of
green and violet light, and there is reason to suspect that
those sensations are always compounded of the separate
sensations combined; at least, this supposition simplifies the
theory of colours. It may, therefore, be adopted with advantage,
until it be found inconsistent with any of the phenomena; and we
may consider white light as composed of a mixture of red, green,
and violet only, ... with respect to the quantity or intensity
of the sensations produced.