Chapter XII: Part 12

_Non-conducting Bodies._--The action that occurs in bodies which
cannot conduct is the most important part of electrical science.
The principle is illustrated by the attraction and repulsion of
an electrified ball of gilt paper by a glass tube, between which
and the ball a sheet of shellac is suspended. The nearer a ball of
another description--an unelectrical insulated body--is brought
to the Leyden jar when charged, the greater influence it is seen
to possess over the gold leaf within the indicator, by induction,
not by conduction. The questions, how electricities attract each
other, what kind of electricity is drawn from the machine to the
hand, how the hand was electric, are thus illustrated. To show the
divers operations of this wonderful force, a tub (a bad conductor)
is placed by the electric machine. When the latter is charged, a
ball, having been electrified from it, is held in the tub, and
rattles against its sides and bottom. On the application of the
ball to the indicator, the gold leaf is shown not to move, whereas
it is agitated manifestly when the same process is gone through
with the exception that the ball is made to touch the outside only
of the tub. Similar experiments with a ball in an ice-pail and
a vessel of wire-gauze, into the latter of which is introduced a
mouse, which is shown to receive no shock, and not to be frightened
at all; while from the outside of the vessel electric sparks are
rapidly produced. This latter demonstration proves that, as the
mouse, so men and women, might be safe inside a building with
proper conductors while lightning played about the exterior. The
wire-gauze being turned inside out, the principle is shown to be
irreversible in spite of the change--what has been the unelectrical
inside of the vessel being now, when made the outside portion,
capable of receiving and transmitting the power, while the original
outside is now unelectrical.

_Repulsion of Bodies._--A remarkable and playful experiment, by
which the repulsion of bodies similarly electrified is illustrated,
consists in placing a basket containing a heap of small pieces
of paper on an insulated stand, and connecting it with the prime
conductor of the electrical machine; when the pieces of paper
rise rapidly after each other into the air, and descend on the
lecture-table like a fall of snow. The effect is greatly increased
when a metal disc is substituted for the basket.

ORIGIN OF THE LEYDEN JAR.

Muschenbroek and Linnæus had made various experiments of a strong kind with water and wire. The former, as appears from a letter of his to Réaumur, filled a small bottle with water, and having corked it up, passed a wire through the cork into the bottle. Having rubbed the vessel on the outside and suspended it to the electric machine, he was surprised to find that on trying to pull the wire out he was subjected to an awfully severe shock in his joints and his whole body, such as he declared he would not suffer again for any experiment. Hence the Leyden jar, which owes its name to the University of Leyden, with which, we believe, Muschenbroek was connected.--_Faraday._

DANGER TO GUNPOWDER MAGAZINES.

By the illustration of a gas globule, which is ignited from a spark by induction, Mr. Faraday has proved in a most interesting manner that the corrugated-iron roofs of some gunpowder-magazines,--on the subject of which he had often been consulted by the builders, with a view to the greater safety of these manufactories,--are absolutely dangerous by the laws of induction; as, by the return of induction, while a storm was discharging itself a mile or two off, a secondary spark might ignite the building.

ARTIFICIAL CRYSTALS AND MINERALS.--“THE CROSSE MITE.”

Among the experimenters on Electricity in our time who have largely contributed to the “Curiosities of Science,” Andrew Crosse is entitled to special notice. In his school-days he became greatly attached to the study of electricity; and on settling on his paternal estate, Fyne Court, on the Quantock Hills in Somersetshire, he there devoted himself to chemistry, mineralogy, and electricity, pursuing his experiments wholly independently of theories, and searching only for facts. In Holwell Cavern, near his residence, he observed the sides and the roof covered with Arragonite crystallisations, when his observations led him to conclude that the crystallisations were the effects, at least to some extent, of electricity. This induced him to make the attempt to form artificial crystals by the same means, which he began in 1807. He took some water from the cave, filled a tumbler, and exposed it to the action of a voltaic battery excited by water alone, letting the platinum-wires of the battery fall on opposite sides of the tumbler from the opposite poles of the battery. After ten days’ constant action, he produced crystals of carbonate of lime; and on repeating the experiment in the dark, he produced them in six days. Thus Mr. Crosse simulated in his laboratory one of the hitherto most mysterious processes of nature.

He pursued this line of research for nearly thirty years at Fyne Court, where his electrical-room and laboratory were on an enormous scale: the apparatus had cost some thousands of pounds, and the house was nearly full of furnaces. He carried an insulated wire above the tops of the trees around his house to the length of a mile and a quarter, afterwards shortened to 1800 feet. By this wire, which was brought into connection with the apparatus in a chamber, he was enabled to see continually the changes in the state of the atmosphere, and could use the fluid so collected for a variety of purposes. In 1816, at a meeting of country gentlemen, he prophesied that, “by means of electrical agency, we shall be able to communicate our thoughts simultaneously with the uttermost ends of the earth.” Still, though he foresaw the powers of the medium, he did not make any experiments in that direction, but confined himself to the endeavour to produce crystals of various kinds. He ultimately obtained forty-one mineral crystals, or minerals uncrystallised, in the form in which they are produced by nature, including one sub-sulphate of copper--an entirely new mineral, neither found in nature nor formed by art previously. His belief was that even diamonds might be produced in this way.

Mr. Crosse worked alone in his retreat until 1836, when, attending the meeting of the British Association at Bristol, he was induced to explain his experiments, for which he was highly complimented by Dr. Buckland, Dr. Dalton, Professor Sedgwick, and others.[51]

Shortly after Mr. Crosse’s return to Fyne Court, while pursuing his experiments for forming crystals from a highly caustic solution out of contact with atmospheric air, he was greatly surprised by the appearance of an insect. Black flint, burnt to redness and reduced to powder, was mixed with carbonate of potash, and exposed to a strong heat for fifteen minutes; and the mixture was poured into a black-lead crucible in an air furnace. It was reduced to powder while warm, mixed with boiling water, kept boiling for some minutes, and then hydrochloric acid was added to supersaturation. After being exposed to voltaic action for twenty-six days, a perfect insect of the Acari tribe made its appearance, and in the course of a few weeks about a hundred more. The experiment was repeated in other chemical fluids with the like results; and Mr. Weeks of Sandwich afterwards produced the Acari inferrocyanerret of potassium. The Acarus of Mr. Crosse was found to contribute a new species of that genus, nearly approaching the Acari found in cheese and flour, or more nearly, Hermann’s _Acarus dimidiatus_.

This discovery occasioned great excitement. The possibility was denied, though Mr. Faraday is said to have stated in the same year that he had seen similar appearances in his own electrical experiments. Mr. Crosse was now accused of impiety and aiming at creation, to which attacks he thus replied:

As to the appearance of the acari under long-continued electrical
action, I have never in thought, word, or deed given any one a
right to suppose that I considered them as a creation, or even as a
formation, from inorganic matter. To create is to form a something
out of a nothing. To annihilate is to reduce that something to
a nothing. Both of these, of course, can only be the attributes
of the Almighty. In fact, I can assure you most sacredly that I
have never dreamed of any theory sufficient to account for their
appearance. I confess that I was not a little surprised, and am so
still, and quite as much as I was when the acari made their first
appearance. Again, I have never claimed any merit as attached to
these experiments. It was a matter of chance; I was looking for
silicious formations, and animal matter appeared instead.

These Acari, if removed from their birthplace, lived and propagated; but uniformly died on the first recurrence of frost, and were entirely destroyed if they fell back into the fluid whence they arose.

One of Mr. Crosse’s visitors thus describes the vast electrical room at Fyne Court:

Here was an immense number of jars and gallipots, containing fluids
on which electricity was operating for the production of crystals.
But you are startled in the midst of your observations by the smart
crackling sound that attends the passage of the electrical spark;
you hear also the rumbling of distant thunder. The rain is already
plashing in great drops against the glass, and the sound of the
passing sparks continues to startle your ear; you see at the window
a huge brass conductor, with a discharging rod near it passing into
the floor, and from the one knob to the other sparks are leaping
with increasing rapidity and noise, every one of which would kill
twenty men at one blow, if they were linked together hand in hand
and the spark sent through the circle. From this conductor wires
pass off without the window, and the electric fluid is conducted
harmlessly away. Mr. Crosse approached the instrument as boldly as
if the flowing stream of fire were a harmless spark. Armed with
his insulated rod, he sent it into his batteries: having charged
them, he showed how wire was melted, dissipated in a moment, by its
passage; how metals--silver, gold, and tin--were inflamed and burnt
like paper, only with most brilliant hues. He showed you a mimic
aurora and a falling-star, and so proved to you the cause of those
beautiful phenomena.

Mr. Crosse appears to have produced in all “about 200 varieties of minerals, exactly resembling in all respects similar ones found in nature.” He tried also a new plan of extracting gold from its ores by an electrical process, which succeeded, but was too expensive for common use. He was in the habit of saying that he could, like Archimedes, move the world “if he were able to construct a battery at once cheap, powerful, and durable.” His process of extracting metals from their ores has been patented. Among his other useful applications of electricity are the purifying by its means of brackish or sea-water, and the improving bad wine and brandy. He agreed with Mr. Quekett in thinking that it is by electrical action that silica and other mineral substances are carried into and assimilated by plants. Negative electricity Mr. Crosse found favourable to no plants except fungi; and positive electricity he ascertained to be injurious to fungi, but favourable to every thing else.

Mr. Crosse died in 1855. His widow has published a very interesting volume of _Memorials_ of the ingenious experimenter, from which we select the following:

On one occasion Mr. Crosse kept a pair of soles under the electric
action for three months; and at the end of that time they were
sent to a friend, whose domestics knew nothing of the experiment.
Before the cook dressed them, her master asked her whether she
thought they were fresh, as he had some doubts. She replied that
she was sure they were fresh; indeed, she said she could swear
that they were alive yesterday! When served at table they appeared
like ordinary fish; but when the family attempted to eat them,
they were found to be perfectly tasteless--the electric action had
taken away all the essential oil, leaving the fish unfit for food.
However, the process is exceedingly useful for keeping fish, meat,
&c. fresh and _good_ for ten days or a fortnight. I have never
heard a satisfactory explanation of the cause of the antiseptic
power communicated to water by the passage of the electric current.
Whether ozone has not something to do with it, may be a question.
The same effect is produced whichever two dissimilar metals are
used.

The Electric Telegraph.

ANTICIPATIONS OF THE ELECTRIC TELEGRAPH.

The great secret of ubiquity, or at least of instantaneous transmission, has ever exercised the ingenuity of mankind in various romantic myths; and the discovery of certain properties of the loadstone gave a new direction to these fancies.

The earliest anticipation of the Electric Telegraph of this purely fabulous character forms the subject of one of the _Prolusiones Academicæ_ of the learned Italian Jesuit Strada, first published at Rome in the year 1617. Of this poem a free translation appeared in 1750. Strada’s fancy was this: “There is,” he supposes, “a species of loadstone which possesses such virtue, that if two needles be touched with it, and then balanced on separate pivots, and the one be turned in a particular direction, the other will sympathetically move parallel to it. He then directs each of these needles to be poised and mounted parallel on a dial having the letters of the alphabet arranged round it. Accordingly, if one person has one of the dials, and another the other, by a little pre-arrangement as to details a correspondence can be maintained between them at any distance by simply pointing the needles to the letters of the required words. Strada, in his poetical reverie, dreamt that some such sympathy might one day be found to hold up the Magnesian Stone.”

Strada’s conceit seems to have made a profound impression on the master-minds of the day. His poem is quoted in many works of the seventeenth and eighteenth centuries; and Bishop Wilkins, in his book on Cryptology, is strangely afraid lest his readers should mistake Strada’s fancy for fact. Wilkins writes: “This invention is altogether imaginary, having no foundation in any real experiment. You may see it frequently confuted in those that treat concerning magnetical virtues.”

Again, Addison, in the 241st No. of the _Spectator_, 1712, describes Strada’s “Chimerical correspondence,” and adds that, “if ever this invention should be revived or put in practice,” he “would propose that upon the lover’s dial-plate there should be written not only the four-and-twenty letters, but several entire words which have always a place in passionate epistles, as flames, darts, die, language, absence, Cupid, heart, eyes, being, drown, and the like. This would very much abridge the lover’s pains in this way of writing a letter, as it would enable him to express the most useful and significant words with a single touch of the needle.”

After Strada and his commentators comes Henry Van Etten, who shows how “Claude, being at Paris, and John at Rome, might converse together, if each had a needle touched by a stone of such virtue that as one moved itself at Paris the other should be moved at Rome:” he adds, “it is a fine invention, but I do not think there is a magnet in the world which has such virtue; besides, it is inexpedient, for treasons would be too frequent and too much protected. (_Recréations Mathématiques_: see 5th edition, Paris, 1660, p. 158.) Sir Thomas Browne refers to this “conceit” as “excellent, and, if the effect would follow, somewhat divine;” but he tried the two needles touched with the same loadstone, and placed in two circles of letters, “one friend keeping one and another the other, and agreeing upon an hour when they will communicate,” and found the tradition a failure that, “at what distance of place soever, when one needle shall be removed unto any letter, the other, by a wonderful sympathy, will move unto the same.” (See _Vulgar Errors_, book ii. ch. iii.)

Glanvill’s _Vanity of Dogmatizing_, a work published in 1661, however, contains the most remarkable allusion to the prevailing telegraphic fancy. Glanvill was an enthusiast, and he clearly predicts the discovery and general adoption of the electric telegraph. “To confer,” he says, “at the distance of the Indies by sympathetic conveyance may be as usual to future times as to us in a literary correspondence.” By the word “sympathetic” he evidently intended to convey magnetic agency; for he subsequently treats of “conference at a distance by impregnated needles,” and describes the device substantially as it is given by Sir Thomas Browne, adding, that though it did not then answer, “by some other such way of magnetic efficiency it may hereafter with success be attempted, when magical history shall be enlarged by riper inspection; and ’tis not unlikely but that present discoveries might be improved to the performance.” This may be said to close the most speculative or mythical period in reference to the subject of electro-telegraphy.

Electricians now began to be sedulous in their experiments upon the new force by friction, then the only known method of generating electricity. In 1729, Stephen Gray, a pensioner of the Charter-house, contrived a method of making electrical signals through a wire 765 feet long; yet this most important experiment did not excite much attention. Next Dr. Watson, of the Royal Society, experimented on the possibility of transmitting electricity through a large circuit from the simple fact of Le Monnier’s account of his feeling the stroke of the electrified fires through two of the basins of the Tuileries (which occupy nearly an acre), by means of an iron chain lying upon the ground and stretched round half their circumference. In 1745, Dr. Watson, assisted by several members of the Royal Society, made a series of experiments to ascertain how far electricity could be conveyed by means of conductors. “They caused the shock to pass across the Thames at Westminster Bridge, the circuit being completed by making use of the river for one part of the chain of communication. One end of the wire communicated with the coating of a charged phial, the other being held by the observer, who in his other hand held an iron rod which he dipped into the river. On the opposite side of the river stood a gentleman, who likewise dipped an iron rod in the river with one hand, and in the other held a wire the extremity of which might be brought into contact with the wire of the phial. Upon making the discharge, the shock was felt simultaneously by both the observers.” (_Priestley’s History of Electricity._) Subsequently the same parties made experiments near Shooter’s Hill, when the wires formed a circuit of four miles, and conveyed the shock with equal facility,--“a distance which without trial,” they observed, “was too great to be credited.”[52] These experiments in 1747 established two great principles: 1, that the electric current is transmissible along nearly two miles and a half of iron wire; 2, that the electric current may be completed by burying the poles in the earth at the above distance.

In the following year, 1748, Benjamin Franklin performed his celebrated experiments on the banks of the Schuylkill, near Philadelphia; which being interrupted by the hot weather, they were concluded by a picnic, when spirits were fired by an electric spark sent through a wire in the river, and a turkey was killed by the electric shock, and roasted by the electric jack before a fire kindled by the electrified bottle.

In the year 1753, there appeared in the _Scots’ Magazine_, vol. xv., definite proposals for the construction of an electric telegraph, requiring as many conducting wires as there are letters in the alphabet; it was also proposed to converse by chimes, by substituting bells for the balls. A similar system of telegraphing was next invented by Joseph Bozolus, a Jesuit, at Rome; and next by the great Italian electrician Tiberius Cavallo, in his treatise on Electricity.

In 1787, Arthur Young, when travelling in France, saw a model working telegraph by M. Lomond: “You write two or three words on a paper,” says Young; “he takes it with him into a room, and turns a machine enclosed in a cylindrical case, at the top of which is an electrometer--a small fine pith-ball; a wire connects with a similar cylinder and electrometer in a distant apartment; and his wife, by remarking the corresponding motions of the ball, writes down the words they indicate: from which it appears that he has formed an alphabet of motions. As the length of the wire makes no difference in the effect, a correspondence might be carried on at any distance. Whatever the use may be, the invention is beautiful.”

We now reach a new epoch in the scientific period--the discovery of the Voltaic Pile. In 1794, according to _Voigt’s Magazine_, Reizen made use of the electric spark for the telegraph; and in 1798 Dr. Salva of Madrid constructed a similar telegraph, which the Prince of Peace subsequently exhibited to the King of Spain with great success.

In 1809, Soemmering exhibited a telegraphic apparatus worked by galvanism before the Academy of Sciences at Munich, in which the mode of signalling consisted in the development of gas-bubbles from the decomposition of water placed in a series of glass tubes, each of which denoted a letter of the alphabet. In 1813, Mr. Sharpe, of Doe Hill near Alfreton, devised a _voltaic_-electric telegraph, which he exhibited to the Lords of the Admiralty, who spoke approvingly of it, but declined to carry it into effect. In the following year, Soemmering exhibited a _voltaic_-electric telegraph of his own construction, which, however, was open to the objection of there being as many wires as signs or letters of the alphabet.

The next invention is of much greater importance. Upon the suggestion of Cavallo, already referred to, Francis Ronalds constructed a perfect electric telegraph, employing frictional electricity notwithstanding Volta’s discoveries had been known in England for sixteen years. This telegraph was exhibited at Hammersmith in 1816:[53] it consisted of a single insulated wire, the indication being by pith-balls in front of a dial. When the wire was charged, the balls were divergent, but collapsed when the wire was discharged; at the same time were employed two clocks, with lettered discs for the signals. “If, as Paley asserts (and Coleridge denies), ‘he alone discovers who proves,’ Ronalds is entitled to the appellation of the first discoverer of an efficient electric telegraph.” (_Saturday Review_, No. 147[54]) Nevertheless the Government of the day refused to avail itself of this admirable contrivance.

In 1819, Oersted made his great discovery of the deflection, by a current of electricity, of a magnetic needle at right angles to such current. Dr. Hamel of St. Petersburg states that Baron Schilling was the first to apply Oersted’s discovery to telegraphy; Ampère had previously suggested it, but his plan was very complicated, and Dr. Hamel maintains that Schilling first realised the idea by actually producing an electro-magnetic telegraph simpler in construction than that which Ampère had _imagined_. In 1836, Professor Muncke of Heidelberg, who had inspected Schilling’s telegraphic apparatus, explained the same to William Fothergill Cooke, who in the following year returned to England, and subsequently, with Professor Wheatstone, laboured simultaneously for the introduction of the electro-magnetic telegraph upon the English railways; the first patent for which was taken out in the joint names of these two gentlemen.

In 1844, Professor Wheatstone, with one of his telegraphs, formed a communication between King’s College and the lofty shot-tower on the opposite bank of the Thames: the wire was laid along the parapets of the terrace of Somerset House and Waterloo Bridge, and thence to the top of the tower, about 150 feet high, where a telegraph was placed; the wire then descended, and a plate of zinc attached to its extremity was plunged into the mud of the river, whilst a similar plate attached to the extremity at the north side was immersed in the water. The circuit was thus completed by the entire breadth of the Thames, and the telegraph acted as well as if the circuit were entirely metallic.

Shortly after this experiment, Professor Wheatstone and Mr. Cooke laid down the first working electric telegraph on the Great Western Railway, from Paddington to Slough.

ELECTRIC GIRDLE FOR THE EARTH.

One of our most profound electricians is reported to have exclaimed: “Give me but an unlimited length of wire, with a small battery, and I will girdle the universe with a sentence in forty minutes.” Yet this is no vain boast; for so rapid is the transition of the electric current along the line of the telegraph wire, that, supposing it were possible to carry the wires eight times round the earth, the transit would occupy but _one second of time_!

CONSUMPTION OF THE ELECTRIC TELEGRAPH.

It is singular to see how this telegraphic agency is measured by the chemical consumption of zinc and acid. Mr. Jones (who has written a work upon the Electric Telegraphs of America) estimates that to work 12,000 miles of telegraph about 3000 zinc cups are used to hold the acid: these weigh about 9000 lbs., and they undergo decomposition by the galvanic action in about six months, so that 18,000 lbs. of zinc are consumed in a year. There are also about 3600 porcelain cups to contain nitric acid; it requires 450 lbs. of acid to charge them once, and the charge is renewed every fortnight, making about 12,000 lbs. of nitric acid in a year.

TIME LOST IN ELECTRIC MESSAGES.

Although it may require an hour, or two or three hours, to transmit a telegraphic message to a distant city, yet it is the mechanical adjustment by the sender and receiver which really absorbs this time; the actual transit is practically instantaneous, and so it would be from here to the antipodes, so far as the current itself is concerned.

THE ELECTRIC TELEGRAPH IN ASTRONOMY AND THE DETERMINATION OF LONGITUDE.

The Electric Telegraph has become an instrument in the hands of the astronomer for determining the difference of longitude between two observatories. Thus in 1854 the difference of longitude between London and Paris was determined within a limit of error which amounted barely to a quarter of a second. The sudden disturbances of the magnetic needle, when freely suspended, which seem to take place simultaneously over whole continents, if not over the whole globe, from some unexplained cause, are pointed out as means by which the differences of longitude between the magnetic observatories may possibly be determined with greater precision than by any yet known method.

So long ago as 1839 Professor Morse suggested some experiments for the determination of Longitudes; and in June 1844 the difference of longitude between Washington and Baltimore was determined by electric means under his direction. Two persons were stationed at these two towns, with clocks carefully adjusted to the respective spots; and a telegraphic signal gave the means of comparing the two clocks at a given instant. In 1847 the relative longitudes of New York, Philadelphia, and Washington were determined by means of the electric telegraph by Messrs. Keith, Walker, and Loomis.

NON-INTERFERENCE OF GALVANIC WAVES ON THE SAME WIRE.

One of the most remarkable facts in the economy of the telegraph is, that the line, when connected with a battery in action, propagates the hydro-galvanic waves in either direction without interference. As several successive syllables of sound may set out in succession from the same place, and be on their way at the same time, to a listener at a distance, so also, where the telegraph-line is long enough, several waves may be on their way from the signal station before the first one reaches the receiving station; two persons at a distance may pronounce several syllables at the same time, and each hear those emitted by the other. So, on a telegraph-line of two or three thousand miles in length in the air, and the same in the ground, two operators may at the same instant commence a series of several dots and lines, and each receive the other’s writings, though the waves have crossed each other on the way.

EFFECT OF LIGHTNING UPON THE ELECTRIC TELEGRAPH.

In the storm of Sunday April 2, 1848, the lightning had a very considerable effect on the wires of the electric telegraph, particularly on the line of railway eastward from Manchester to Normanton. Not only were the needles greatly deflected, and their power of answering to the handles considerably weakened, but those at the Normanton station were found to have had their poles reversed by some action of the electric fluid in the atmosphere. The damage, however, was soon repaired, and the needles again put in good working order.

ELECTRO-TELEGRAPHIC MESSAGE TO THE STARS.

The electric fluid travels at the mean rate of 20,000 miles in a second under ordinary circumstances; therefore, if it were possible to establish a telegraphic communication with the star 61 Cygni, it would require ninety years to send a message there.

Professor Henderson and Mr. Maclear have fully confirmed the annual parallax of α Centauri to amount to a second of arc, which gives about twenty billions of miles as its distance from our system; a ray of light would arrive from α Centauri to us in little more than three years, and a telegraphic despatch would arrive there in thirty years.

THE ATLANTIC TELEGRAPH.

The telegraphic communication between England and the United States is so grand a conception, that it would be impossible to detail its scientific and mechanical relations within the limits of the present work. All that we shall attempt, therefore, will be to glance at a few of the leading operations.

In the experiments made before the Atlantic Telegraph was finally decided on, 2000 miles of subterranean and submarine telegraphic wires, ramifying through England and Ireland and under the waters of the Irish Sea, were specially connected for the purpose; and through this distance of 2000 miles 250 distinct signals were recorded and printed in one minute.

First, as to the _Cable_. In the ordinary wires by the side of a railway the electric current travels on with the speed of lightning--uninterrupted by the speed of lightning; but when a wire is encased in gutta-percha, or any similar covering, for submersion in the sea, new forces come into play. The electric excitement of the wire acts by induction, through the envelope, upon the particles of water in contact with that envelope, and calls up an electric force of an opposite kind. There are two forces, in fact, pulling against each other through the gutta-percha as a neutral medium,--that is, the electricity in the wire, and the opposite electricity in the film of water immediately surrounding the cable; and to that extent the power of the current in the enclosed wire is weakened. A submarine cable, when in the water, is virtually _a lengthened-out Leyden jar_; it transmits signals while being charged and discharged, instead of merely allowing a stream to flow evenly along it: it is a _bottle_ for holding electricity rather than a _pipe_ for carrying it; and this has to be filled for every time of using. The wire being carried underground, or through the water, the speed becomes quite measurable, say a thousand miles in a second, instead of two hundred thousand, owing to the retardation by induced or retrograde currents. The energy of the currents and the quality of the wire also affect the speed. Until lately it was supposed that the wire acts only as a _conductor_ of electricity, and that a long wire must produce a weaker effect than a short one, on account of the consequent attenuation of the electrical influence; but it is now known that, the cable being a _reservoir_ as well as a conductor, its electrical supply is increased in proportion to its length.

The electro-magnetic current is employed, since it possesses a treble velocity of transmission, and realises consequently _a threefold working speed_ as compared with simple voltaic electricity. Mr. Wildman Whitehouse has determined by his ingenious apparatus that the speed of the voltaic current might be raised under special circumstances to 1800 miles per second; but that of the induced current, or the electro-magnetic, might be augmented to 6000 miles per second.

Next as to a _Quantity Battery_ employed in these investigations. To effect a charge, and transmit a current through some thousand miles of the Atlantic Cable, Mr. Whitehouse had a piece of apparatus prepared consisting of twenty-five pairs of zinc and silver plates about the 20th part of a square inch large, and the pairs so arranged that they would hold a drop of acidulated water or brine between them. On charging this Lilliputian battery by dipping the plates in salt and water, messages were sent from it through a thousand miles of cable with the utmost ease; and not only so,--pair after pair was dropped out from the series, the messages being still sent on with equal facility, until at last only a single pair, charged by one single drop of liquid, was used. Strange to say, with this single pair and single drop distinct signals were effected through the thousand miles of the cable! Each signal was registered at the end of the cable in less than three seconds of time.

The entire length of wire, iron and copper, spun into the cable amounts to 332,500 miles, a length sufficient to engirdle the earth thirteen times. The cable weighs from 19 cwt. to a ton per mile, and will bear a strain of 5 tons.

The _Perpetual Maintenance Battery_, for working the cable at the bottom of the sea, consists of large plates of platinated silver and amalgamated zinc, mounted in cells of gutta-percha. The zinc plates in each cell rest upon a longitudinal bar at the bottom, and the silver plates hang upon a similar bar at the top of the cell; so that there is virtually but a single stretch of silver and a single stretch of zinc in operation. Each of the ten cells contains 2000 square inches of acting surface; and the combination is so powerful, that when the broad strips of copper-plate which form the polar extensions are brought into contact or separated, brilliant flashes are produced, accompanied by a loud crackling sound. The points of large pliers are made red-hot in five seconds when placed between them, and even screws burn with vivid scintillation. The cost of maintaining this magnificent ten-celled Titan battery at work does not exceed a shilling per hour. The voltaic current generated in this battery is not, however, the electric stream to be sent across the Atlantic, but is only the primary power used to call up and stimulate the energy of a more speedy traveller by a complicated apparatus of “Double Induction Coils.” Nor is the transmission-current generated in the inner wire of the double induction coil,--and which becomes weakened when it has passed through 1800 or 1900 miles,--set to work to print or record the signals transmitted. This weakened current merely opens and closes the outlet of a fresh battery, which is to do the printing labour. This relay-instrument (as it is called), which consists of a temporary and permanent magnet, is so sensitive an apparatus, that it may be put in action by a fragment of zinc and a sixpence pressed against the tongue.

The attempts to lay the cable in August 1857 failed through stretching it so tightly that it snapped and went to the bottom, at a depth of 12,000 feet, forty times the height of St. Paul’s.

This great work was resumed in August 1858; and on the 5th the first signals were received through _two thousand and fifty miles_ of the Atlantic Cable. And it is worthy of remark, that just 111 years previously, on the 5th of August 1747, Dr. Watson astonished the scientific world by practically proving that the electric current could be transmitted through a _wire hardly two miles and a half long_.[55]

Miscellanea.

HOW MARINE CHRONOMETERS ARE RATED AT THE ROYAL OBSERVATORY, GREENWICH.

The determination of the Longitude at Sea requires simply accurate instruments for the measurement of the positions of the heavenly bodies, and one or other of the two following,--either perfectly correct watches--or chronometers, as they are now called--or perfectly accurate tables of the lunar motions.

So early as 1696 a report was spread among the members of the Royal Society that Sir Isaac Newton was occupied with the problem of finding the longitude at sea; but the rumour having no foundation, he requested Halley to acquaint the members “that he was not about it.”[56] (_Sir David Brewster’s Life of Newton._)

In 1714 the legislature of Queen Anne passed an Act offering a reward of 20,000_l._ for the discovery of the longitude, the problem being then very inaccurately solved for want of good watches or lunar tables. About the year 1749, the attention of the Royal Society was directed to the improvements effected in the construction of watches by John Harrison, who received for his inventions the Copley Medal. Thus encouraged, Harrison continued his labours with unwearied diligence, and produced in 1758 a timekeeper which was sent for trial on a voyage to Jamaica. After 161 days the error of the instrument was only 1m 5s, and the maker received from the nation 5000_l._ The Commissioners of the Board of Longitude subsequently required Harrison to construct under their inspection chronometers of a similar nature, which were subjected to trial in a voyage to Barbadoes, and performed with such accuracy, that, after having fully explained the principle of their construction to the commissioners, they awarded him 10,000_l._ more; at the same time Euler of Berlin and the heirs of Mayer of Göttingen received each 3000_l._ for their lunar tables.

The account of the trial of Harrison’s watch is very interesting.
In April 1766, by desire of the Commissioners of the Board, the
Lords of the Admiralty delivered the watch into the custody of
the Astronomer-Royal, the Rev. Dr. Nevil Maskelyne. It was then
placed at the Royal Observatory at Greenwich, in a box having two
different locks, fixed to the floor or wainscot, with a plate of
glass in the lid of the box, so that it might be compared as often
as convenient with the regulator and the variation set down. The
form observed by Mr. Harrison in winding up the watch was exactly
followed; and an officer of Greenwich Hospital attended every day,
at a stated hour, to see the watch wound up, and its comparison
with the regulator entered. A key to one of the locks was kept at
the Hospital for the use of the officer, and the other remained
at the Observatory for the use of the Astronomer-Royal or his
assistant.

The watch was then tried in various positions till the beginning
of July; and from thence to the end of February following in a
horizontal position with its face upwards.

The variation of the watch was then noted down, and a register was
kept of the barometer and thermometer; and the time of comparing
the same with the regulator was regularly kept, and attested by
the Astronomer-Royal or his assistant and such of the officers as
witnessed the winding-up and comparison of the watch.

Under these conditions Harrison’s watch was received by the
Astronomer-Royal at the Admiralty on May 5, 1766, in the presence
of Philip Stephens, Esq., Secretary of the Admiralty; Captain
Baillie, of the Royal Hospital, Greenwich; and Mr. Kendal the
watchmaker, who accompanied the Astronomer-Royal to Greenwich, and
saw the watch started and locked up in the box provided for it. The
watch was then compared with the transit clock daily, and wound up
in the presence of the officer of Greenwich Hospital. From May 5 to
May 17 the watch was kept in a horizontal position with its face
upwards; from May 18 to July 6 it was tried--first inclined at an
angle of 20° to the horizon, with the face upwards, and the hours
12, 6, 3, and 9, highest successively; then in a vertical position,
with the same hours highest in order; lastly, in a horizontal
position with the face downwards. From July 16, 1766, to March 4,
1767, it was always kept in a horizontal position with its face
upwards, lying upon the same cushion, and in the same box in which
Mr. Harrison had kept it in the voyage to Barbadoes.

From the observed transits of the sun over the meridian, according
to the time of the regulator of the Observatory, together with
the attested comparisons of Mr. Harrison’s watch with the transit
clock, the watch was found too fast on several days as follows:

h. m. s.
1766. May 6 too fast 0 0 16·2
May 17 ” 0 3 51·8
July 6 ” 0 14 14·0
Aug. 6 ” 0 23 58·4
Sept. 17 ” 0 32 15·6
Oct. 29 ” 0 42 20·9
Dec. 10 ” 0 54 46·8
1767. Jan. 21 ” 1 0 28·6
March 4 ” 1 11 23·0

From May 6, which was the day after the watch arrived at the Royal
Observatory, to March 4, 1767, there were six periods of six weeks
each in which the watch was tried in a horizontal position; when
the gaining in these several periods was as follows:

During the first 6 weeks it gained 13m 20s, answering to 3° 20′
of longitude.

In the 2d period of 6
weeks (from Aug. 6 to ” 8 17 ” 2 4
Sept. 17)

In the 3d period (from ” 10 5 ” 2 31
Sept. 17 to Oct. 29)

In the 4th period (from ” 12 26 ” 3 6
Oct. 29 to Dec. 20)

In the 5th period (from ” 5 42 ” 1 25
Dec. 20 to Jan. 21)

In the 6th period (from ” 10 54 ” 2 43
Jan. 21 to Mar. 4)

It was thence concluded that Mr. Harrison’s watch could not be depended upon to keep the longitude within a West-India voyage of six weeks, nor to keep the longitude within half a degree for more than a fortnight; and that it must be kept in a place where the temperature was always some degrees above freezing.[57] (However, Harrison’s watch, which was made by Mr. Kendal subsequently, succeeded so completely, that after it had been round the world with Captain Cook, in the years 1772-1775, the second 10,000_l._ was given to Harrison.)

In the Act of 12th Queen Anne, the comparison of chronometers was not mentioned in reference to the Observatory duties; but after this time they became a serious charge upon the Observatory, which, it must be admitted, is by far the best place to try chronometers: the excellence of the instruments, and the frequent observations of the heavenly bodies over the meridian, will always render the rate of going of the Observatory clock better known than can be expected of the clock in most other places.

After Mr. Harrison’s watch was tried, some watches by Earnshaw, Mudge, and others, were rated and examined by the Astronomer-Royal.

At the Royal Observatory, Greenwich, there are frequently above 100 chronometers being rated, and there have been as many as 170 at one time. They are rated daily by two observers, the process being as follows. At a certain time every day two assistants in charge repair to the chronometer-room, where is a time-piece set to true time; one winds up each with its own key, and the second follows after some little time and verifies the fact that each is wound. One assistant then looks at each watch in succession, counting the beats of the clock whilst he compares the chronometer by the eye; and in the course of a few seconds he calls out the second shown by the chronometer when the clock is at a whole minute. This number is entered in a book by the other assistant, and so on till all the chronometers are compared. Then the assistants change places, the second comparing and the first writing down. From these daily comparisons the daily rates are deduced, by which the goodness of the watch is determined. The errors are of two classes--that of general bad workmanship, and that of over or under correction for temperature. In the room is an apparatus in which the watch may be continually kept at temperatures exceeding 100° by artificial heat; and outside the window of the room is an iron cage, in which they are subjected to low temperatures. The very great care taken with all chronometers sent to the Royal Observatory, as well as the perfect impartiality of the examination which each receives, afford encouragement to their manufacture, and are of the utmost importance to the safety and perfection of navigation.

We have before us now the Report of the Astronomer-Royal on the Rates of Chronometers in the year 1854, in which the following are the successive weekly sums of the daily rates of the first there mentioned:

Week ending secs.

Jan. 21, loss in the week 2·2
” 28 ” 4·0
Feb. 4 ” 1·1
” 11 ” 5·0
” 18 ” 4·9
” 25 ” 5·5
Mar. 4 ” 6·0
” 11 ” 6·0
” 18 ” 1·5
” 25 ” 4·5
Apr. 1 ” 4·0
” 8 ” 1·5
” 15, gain in the week 0·4
Apr. 22, ” 2·6
” 29, loss in the week 1·4
May 6 ” 2·1
” 13 ” 3·0
” 20 ” 5·1
” 27 ” 3·3
June 3 ” 2·8
” 10 ” 1·8
” 17 ” 2·0
” 24 ” 3·0
July 1 ” 2·5
” 8 ” 1·2

Till February 4 the watch was exposed to the external air outside a north window; from February 5 to March 4 it was placed in the chamber of a stove heated by gas to a moderate temperature; and from April 29 to May 20 it was placed in the chamber when heated to a high temperature.

The advance in making chronometers since Harrison’s celebrated watch was tried at the Royal Observatory, more than ninety years since, may be judged by comparing its rates with those above.

GEOMETRY OF SHELLS.

There is a mechanical uniformity observable in the description of shells of the same species which at once suggests the probability that the generating figure of each increases, and that the spiral chamber of each expands itself, according to some simple geometrical law common to all. To the determination of this law the operculum lends itself, in certain classes of shells, with remarkable facility. Continually enlarged by the animal, as the construction of its shell advances so as to fill up its mouth, the operculum measures the progressive widening of the spiral chamber by the progressive stages of its growth.

* * * * *

The animal, as he advances in the construction of his shell, increases continually his operculum, so as to adjust it to his mouth. He increases it, however, not by additions made at the same time all round its margin, but by additions made only on one side of it at once. One edge of the operculum thus remains unaltered as it is advanced into each new position, and placed in a newly-formed section of the chamber similar to the last but greater than it.

That the same edge which fitted a portion of the first less section should be capable of adjustment so as to fit a portion of the next similar but greater section, supposes a geometrical provision in the curved form of the chamber of great complication and difficulty. But God hath bestowed upon this humble architect the practical skill of the learned geometrician; and he makes this provision with admirable precision in that curvature of the logarithmic spiral which he gives to the section of the shell. This curvature obtaining, he has only to turn his operculum slightly round in its own place, as he advances it into each newly-formed portion of his chamber, to adapt one margin of it to a new and larger surface and a different curvature, leaving the space to be filled up by increasing the operculum wholly on the outer margin.

* * * * *

Why the Mollusks, who inhabit turbinated and discoid shells, should, in the progressive increase of their spiral dwellings, affect the peculiar law of the logarithmic spiral, is easily to be understood. Providence has subjected the instinct which shapes out each to a rigid uniformity of operation.--_Professor Mosely_: _Philos. Trans._ 1838.

HYDRAULIC THEORY OF SHELLS.

How beautifully is the wisdom of God developed in shaping out and moulding shells! and especially in the particular value of the constant angle which the spiral of each species of shell affects,--a value connected by a necessary relation with the economy of the material of each, and with its stability and the conditions of its buoyancy. Thus the shell of the _Nautilus Pompilius_ has, hydrostatically, an A-statical surface. If placed with any portion of its surface upon the water, it will immediately turn over towards its smaller end, and rest only on its mouth. Those conversant with the theory of floating bodies will recognise in this an interesting property.--_Ibid._

SERVICES OF SEA-SHELLS AND ANIMALCULES.

Dr. Maury is disposed to regard these beings as having much to do in maintaining the harmonies of creation, and the principles of the most admirable compensation in the system of oceanic circulation. “We may even regard them as regulators, to some extent, of climates in parts of the earth far removed from their presence. There is something suggestive both of the grand and the beautiful in the idea that while the insects of the sea are building up their coral islands in the perpetual summer of the tropics, they are also engaged in dispensing warmth to distant parts of the earth, and in mitigating the severe cold of the polar winter.”

DEPTH OF THE PRIMEVAL SEAS.

Professor Forbes, in a communication to the Royal Society, states that not only the colour of the shells of existing mollusks ceases to be strongly marked at considerable depths, but also that well-defined patterns are, with very few and slight exceptions, presented only by testacea inhabiting the littoral, circumlittoral, and median zones. In the Mediterranean, only one in eighteen of the shells taken from below 100 fathoms exhibit any markings of colour, and even the few that do so are questionable inhabitants of those depths. Between 30 and 35 fathoms, the proportion of marked to plain shells is rather less than one in three; and between the margin and two fathoms the striped or mottled species exceed one-half of the total number. In our own seas, Professor Forbes observes that testacea taken from below 100 fathoms, even when they are individuals of species vividly striped or banded in shallower zones, are quite white or colourless. At between 60 and 80 fathoms, striping and banding are rarely presented by our shells, especially in the northern provinces; from 50 fathoms, shallow bands, colours, and patterns, are well marked. _The relation of these arrangements of colour to the degree of light penetrating the different zones of depth_ is a subject well worthy of minute inquiry.

NATURAL WATER-PURIFIERS.

Mr. Warrington kept for a whole year twelve gallons of water in a state of admirably balanced purity by the following beautiful action:

In the tank, or aquarium, were two gold fish, six water-snails, and
two or three specimens of that elegant aquatic plant _Valisperia
sporalis_, which, before the introduction of the water-snails, by
its decayed leaves caused a growth of slimy mucus, and made the
water turbid and likely to destroy both plants and fish. But under
the improved arrangement the slime, as fast as it was engendered,
was consumed by the water-snails, which reproduced it in the shape
of young snails, which furnished a succulent food to the fish.
Meanwhile the _Valisperia_ plants absorbed the carbonic acid
exhaled by the respiration of their companions, fixing the carbon
in their growing stems and luxuriant blossoms, and refreshing
the oxygen (during sunshine in visible little streams) for the
respiration of the snails and the fish. The spectacle of perfect
equilibrium thus simply maintained between animal, vegetable, and
inorganic activity, was strikingly beautiful; and such means might
possibly hereafter be made available on a large scale for keeping
tanked water sweet and clean.--_Quarterly Review_, 1850.

HOW TO IMITATE SEA-WATER.