SECTION 12.MISCELLANEA.

Moon’s Phases.—It has been shown that the Moon is not a reflector of the Sun’s light, but is self-luminous. That the luminosity is confined to one-half its surface is sufficiently shown by the fact that at “New Moon” the whole circle or outline of the Moon is often distinctly visible; but the darker outline is less, or the circle is smaller than the segment which is illuminated. From this it is easily seen that “New Moon,” “Full Moon,” and “Gibbous Moon” are but the different proportions of the illuminated surface which are presented to the observer on earth.

Moon’s Appearance.—Astronomers have indulged their imagination to such a degree that the Moon has been considered to be a solid, opaque, spherical world, having mountains, valleys, lakes, volcanic craters, and other conditions analogous to the surface of the earth. So far has this fancy been carried, that the whole visible disc has been mapped out, and special names given to its various peculiarities, asthough they had been carefully observed and measured by a party of terrestrial ordnance surveyors. All this has been done in direct opposition to the fact that whoever looks, without previous bias, through a powerful telescope at the Moon’s surface, will be puzzled to say what it is really like, or how to compare it with anything known. The comparison which may be made, will depend greatly upon the state of mind of the observer. It is well known that persons looking at the rough bark of a tree, or at the irregular lines or veins in certain kinds of marble and stone, or gazing at the red embers in a dull fire, will, according to the degree of activity of the imagination, be able to see different forms, even the outlines of animals and human faces. It is in this way that persons may fancy that the Moon’s surface is broken up into hills and valleys and other arrangements such as are found on earth. But that anything really similar to the surface of our own world is anywhere visible upon the Moon is altogether fallacious. This is admitted by some of those who have written upon the subject “Some persons when they look into a telescope for the first time, having heard that mountains are to be seen, and discovering nothing but these (previously described) unmeaning figures, break off indisappointment, and have their faith in these things rather diminished than increased. I would advise, therefore, before the student takes even hisfirst viewof the Moon through a telescope, to form as clear an idea as he can how mountains, and valleys, and caverns situated at such a distanceoughtto look, and by what marks they may be recognised. Let him seize, if possible, the most favourable periods (about the time of the first quarter), and previouslylearn from drawingsand explanations how tointerpreteverything he sees.”[31]“Whenever we exhibit celestial objects to inexperienced observers it is usual to precede the view with gooddrawingsof the objects, accompanied by an explanation of what each appearance exhibited in the telescopeindicates. The novice is told that mountains and valleys can be seen in the Moon by the aid of the telescope; but on looking he sees a confused mass of light and shade, andnothingwhichlooksto himlike either mountains or valleys! Had his attention been previously directed to a plaindrawingof the Moon, and each particular appearanceinterpretedto him, he would then have looked through the telescope with intelligence and satisfaction!”[32]Thus it isadmitted by those who teach that the Moon is a spherical world, having hills and dales like the earth, can only see such things in imagination. “Nothing but unmeaning figures” are really visible, and “the students break off in disappointment, and have their faith in such things rather diminished than increased,” “until they previously learn fromdrawingsand explanations how tointerpreteverything seen.” But whofirst madethe drawings? Whofirst interpretedthe “unmeaning figures” and the “confused mass of light and shade?” Who first declared them to indicate mountains and valleys, and ventured to make drawings and give explanations and interpretations for the purpose of biasing the minds, and fixing or guiding the imaginations of subsequent observers? Whoever they were, they at least had “given the reins to Fancy,” and afterwards took upon themselves to dogmatise and teach their crude and unwarranted imaginings to succeeding investigators. And this is the kind of evidence and “reasoning” which is obtruded in our seats of learning, and spread out in the numerous works which are published for the edification of society!

[31]“Mechanism of the Heavens,” by Denison Olmsted, LL.D., Professor of Natural Philosophy and Astronomy in Gale College, U.S.[32]Mitchell’s “Orbs of Heaven,” p. 232.

[31]“Mechanism of the Heavens,” by Denison Olmsted, LL.D., Professor of Natural Philosophy and Astronomy in Gale College, U.S.

[32]Mitchell’s “Orbs of Heaven,” p. 232.

The Planet Neptune.—For some years the advocates of the earth’s rotundity, and of the Newtonian philosophy generally, were accustomed to refer with an air of pride and triumphto the discovery of a new planet, which was called Neptune, as an undeniable evidence of the truth of their system or theory. The existence of this luminary was said to have been predicated from calculation only, and for a considerable period before it had been seen by the telescope. It was urged that therefore the system which would permit of such a discovery must be true. But the whole matter subsequently proved to be unsatisfactory. That a proper conception may be formed of the actual value of the calculations and their supposed verification, the following account will be useful. “In the year 1781, on March 13, Uranus was discovered by Sir William Herschel, who was examining some small stars near the feet of Gemini; and he observed one of them to have a sensible amount of diameter and less brightness than the others, and it was soon found to be a planet. It, however, had been seen before—first, by Flamstead, on December 23rd, 1690; and between this time and 1781 it had been observed 16 times by Flamstead, Bradley, Mayer, and Lemonnier; these astronomers had classed it as a star of the sixth magnitude. Between 1781 and 1820 it was of course very frequently observed; and it was hoped that at the latter time sufficient data existed to construct accurate tables of its motions. This task was undertakenby M. Bouvard, Memberde L’Academie des Sciences, but he met with unforeseen difficulties. It was found utterly impossible to construct tables which would represent the 17 ancient observations, and at the same time the more numerous modern ones; and it was finally concluded that the ancient observations were erroneous, or that some strange and unknown action disturbed, or had disturbed, the planet; consequently M. Bouvard discarded entirely the old observations, and used only those taken between 1781 and 1820, in constructing the tables of Uranus. For some years past it has been found that the tables thus constructed do not agree any better with modern observations, than they do with the ancient observations;consequently it was evident that the planet was under the influence of some unknown cause. Several hypotheses have been suggested as to the nature of this cause; some persons talked of a resisting medium; others of a great satellite which might accompany Uranus; some even went so far as to suppose that the vast distance Uranus is from the Sun caused the law of gravitation to lose some of its force; others thought that the rapid flight of a comet had disturbed its regular movements; others thought of the existence of a planet beyond Uranus, whose disturbing force caused the anomalousmotions of the planet; but no one did otherwise than follow the bent of his inclination, and did not support his assertion by any positive considerations.

“Thus was the theory of Uranus surrounded with difficulties, when M. Le Verrier, an eminent French mathematician, undertook to investigate the irregularities in its motions. His first paper appeared on the 10th November, 1845, and his second on June 1, 1846 (published in the Comptes Rendûs). In this second paper, after a most elaborate and careful investigation, he proves the utter incompatibility of any of the preceding hypotheses to account for the planet’s motions, except only that of the last one, viz., that of a new planet. He then successively proves that this planet cannot be situated either between the Sun and Saturn, or between Saturn and Uranus; but that it must be beyond Uranus. And in this paper he asks the following questions:—‘Is it possible that the irregularities of Uranus can be owing to the action of a planet situated in the ecliptic, at a distance of twice the mean distance of Uranus from the Sun? If so, where is it actually situated? What is its mass? What are the elements of the orbit it describes?”

This was the problem he set himself to work upon, by the means of solving the inverse problem of the perturbations; for instead ofhaving to measure the action of a determined planet, he had to deduce the elements of the orbit of the disturbing planet, and its place in the heavens from the recognised inequalities of Uranus. And this problem M. Le Verrier has successfully solved. In his second paper he deduces the place in the heavens that the body must be as 325° of helio-centric longitude. On the 31st August last he published his third paper. In this he has calculated that the period of the planet is 217 years; and that it moves in an orbit at the distance of more than 3,000 millions of miles from the Sun; that its mean longitude on January 1st, 1847, will be 318° 17′; its true longitude 326° 32′; and that the longitude of its perihelion will be 284° 45′; that it will appear to have a diameter of 3¹⁄₄ seconds of arc as seen from the earth; and that it is now about 5° E. ofDelta Capricorni.

“These remarkable calculations have pointed out a position which has very nearly proved to be the true one.

“On September 23, Dr. Galle at Berlin discovered a star of the eighth magnitude, which has proved to be the planet. Its place at the time was five degrees fromDelta Capricorni. It was found to have a disc of 3 seconds as predicted; and its longitude at the time differs less than a degree from the longitude computedfrom the above elements. Its daily motion, too, is found to agree very closely with the predicted; and, judging from this last circumstance, the planet’s distance, as stated above, must be nearly the truth.

“Thus the result of these calculations was the discovery of a new planet in the place assigned to it by theory, whose mass, distance, position in the heavens, and orbit it describes round the Sun, were all approximately determined before the planet had ever been seen; and all agrees with observations, so far as can at present be determined. It is found to have a disc, and its diameter cannot be much less than 40,000 miles, and may be more; its motions are very slow; it is at present in the constellation of Aquarius as indicated by theory; and it will be in the constellation of Capricornus all the year 1847. It may be readily seen in a telescope of moderate power.

“Whatever view we take of this noble discovery it is most gratifying, whether at the addition of another planet to our list; whether at the proving the correctness of the theory of universal gravitation; or in what view soever, it must be considered as a splendid discovery, and the merit is chiefly due to theoretical astronomy. This discovery is perhaps the greatest triumphof astronomical science that has ever been recorded.”[33]

[33]“Illustrated London Almanack for 1847.”

If such things as criticism, experience, and comparative observation did not exist, the tone of exultation in which the above article indulges might be properly shared in by the astronomical student; but let the following extracts be carefully read, and it will be seen that such a tone was premature and unwarranted. “Paris, Sept. 15, 1848. The only sittings of the Academy of late in which there was anything worth recording, and even this was not of a practical character, were those of the 29th ult. and the 11th inst. On the former day M. Babinet made a communication respecting the planet Neptune, which has been generally called M. Le Verrier’s planet, the discovery of it having, as it was said, been made by him from theoretical deductions, which astonished and delighted the scientific public. What M. Le Verrier had inferred from the action on other planets of some body which ought to exist was verified, at least so it was thought at the time, by actual vision. Neptune was actually seen by other astronomers, and the honour of the theorist obtained additional luster. But it appears from a communication of M. Babinet thatthis is not the planetof M. Le Verrier. He had placed his planet at a distancefrom the Sun equal to thirty-six times the limit of the terrestrial orbit; Neptune revolves at a distance equal to thirty times of these limits, which makes a difference of nearlytwo hundred millions of leagues! M. Le Verrier had assigned to his planet a body equal to thirty-eight times that of the earth; Neptune has onlyone thirdof this volume! M. Le Verrier had stated the revolutions of his planet round the Sun to take place in two hundred and seventeen years; Neptune performs its revolutions in one hundred and sixty-six years! Thus then Neptune is not M. Le Verrier’s planet; and all his theory as regards that planet falls to the ground! M. Le Verrier may find another planet, but it will not answer the calculations which he had made for Neptune. In the sitting of the 14th, M. Le Verrier noticed the communication of M. Babinet, and to a great extent admitted his own error! He complained indeed that much of what he said was taken in too absolute a sense; but he evinces much more candour than might have been expected from a disappointed explorer. M. Le Verrier may console himself with the reflection that if he has not been so successful as he thought he had been, others might have been equally unsuccessful, and as he has still before him an immense field for the exercise of observation and calculation, wemay hope that he will soon make some discovery which will remove the vexation of his present disappointment.”[34]

[34]“Times” Newspaper, Monday, Sept. 18, 1848.

“As the data of Le Verrier and Adams stand at present there is a discrepancy between the predicted and the true distance; and in some other elements of the planet. It remains, therefore, for these or future astronomers to reconcile theory with fact; or, perhaps, as in the case of Uranus, to make the new planet the means of leading to yet greater discoveries. It would appear, from the most recent observations, that the mass of Neptune, instead of being as at first stated one nine thousand three hundredth is only one twenty three thousandth that of the Sun; whilst its periodic time is now given with a greater probability at 166 years; and its mean distance from the Sun nearly thirty. Le Verrier gave the mean distance from the Sun thirty-six times that of the Earth; and the period of revolution 217 years.[35]

[35]“Cosmos,” by Humboldt, p. 75.

“May 14, 1847. A Paper was read before the Royal Astronomical Society, by Professor Schumacher, ‘on the identity of the planet Neptune (M. Le Verrier’s) with a star observed by M. Lalande in May, 1795.’”[36]

[36]“Report of Royal Astronomical Society,” for Feb. 11, 1848, No. 4, vol. 8.

Such mistakes as the above ought at least to make the advocates of the Newtonian theory less positive, and more ready to acknowledge that at best their system is but hypothetical and must sooner or later give place to a philosophy the premises of which are demonstrable, and which is in all its details sequent and consistent.

In the early part of the year 1851, the scientific journals and nearly all the newspapers published in Great Britain and on the Continents of Europe and America were occupied in recording and discussing certain experiments with the pendulum, first made by M. Foucault, of Paris; and the public were startled by the announcement that the results furnished a practical proof of the Earth’s rotation.

The subject was referred to in theLiterary Gazette, in the following words:—“Everybody knows what is meant by a pendulum in its simplest form, a weight hanging by a thread to a fixed point. Such was the pendulum experimented upon long ago by Galileo, who discovered the well-known law of isochronous vibrations, applicable to the same. The subject has sincereceived a thorough examination, as well theoretical as practical, from mathematicians and mechanicians; and yet, strange to say, the most remarkable feature of the phenomenon has remained unobserved and wholly unsuspected until within the last few weeks, when a young and promising French physicist, M. Foucault, who was induced by certain reflections to repeat Galileo’s experiments in the cellar of his mother’s house at Paris, succeeded in establishing the existence of a fact connected with it which gives an immediate and visible demonstration of the Earth’s rotation. Suppose the pendulum already described to be set moving in a vertical plane from north to south, the plane in which it vibrates, to ordinary observation, would appear to be stationary. M. Foucault, however, has succeeded in showing that this is not the case, but that the plane is itself slowly moving round the fixed point as a centre in a direction contrary to the Earth’s rotation,i.e., with the apparent heavens, from east to west. His experiments have since been repeated in the hall of the observatory, under the superintendence of M. Arago, and fully confirmed. If a pointer be attached to the weight of a pendulum suspended by a long and fine wire, capable of turning round in all directions, and nearly in contact with the floor of a room, the line which thispointer appears to trace on the ground, and which may easily be followed by a chalk mark, will be found to be slowly, but visibly, and constantly moving round, like the hand of a watch dial; and the least consideration will show that this ought to be the case, and will excite astonishment that so simple a consequence as this is, of the most elementary laws of Geometry and Mechanics, should so long have remained unobserved. * * * The subject has created a great sensation in the mathematical and physical circles of Paris. It is proposed to obtain permission from the Government to carry on further observations by means of a pendulum suspended from the dome of the Pantheon, length of suspension being a desideratum in order to make the result visible on a larger scale, and secure greater constancy and duration in the experiment. The time required for the performance of a complete revolution of the plane of vibration would be about 32 hours 8 minutes for the parallel of Paris; 30 hours 40 minutes for that of London; and at 30 degrees from the equator exactly 48 hours. Certainly any one who should have proposed not many weeks back to prove the rotation of the Earth upon which we stand by means of direct experiment made upon its surface would have run the risk, with the mob of gentlemen who write upon mechanics, of beingthought as mad as if he were to have proposed reviving Bishop Wilkins’s notable plan for going to the North American colonies in a few hours, by rising in a balloon from the Earth and gently floating in the air until the Earth, in its diurnal rotation, have turned the desired quarter towards the suspended æronaut, whereupon as gently to descend; so necessary and wholesome is it occasionally to reconsider the apparently simplest and best established conclusions of science.”

The following is from theScotsman, which has always been distinguished for the accuracy of its scientific papers. The article bears the initials “C. M.,” which will at once be recognised as those of Mr. Charles Maclaren, for many years the accomplished editor of that journal:—“The beautiful experiment contrived by M. Foucault to demonstrate the rotation of the globe, has deservedly excited universal interest. * * * A desire has always been felt that some method could be devised of rendering this rotation palpable to the senses. Even the illustrious Laplace participated in this feeling and has left it on record. ‘Although,’ he says, ‘the rotation of the Earth is now established with all the certainty which the physical sciences require, still a direct proof of that phenomenon ought to interest both geometricians and astronomers.’ No man ever knew the laws of the planetarymotions better than Laplace, and before penning such a sentence, it is probable that he had turned the subject in his mind, and without discovering any process by which the object could be attained; but it does not follow that if he had applied the whole force of his genius to the task, he would not have succeeded. Be this as it may, here we have the problem solved by a man not probably possessing a tithe of his science or talent; and, what is very remarkable, after the discovery was made, it was found to be legitimately deducible from mathematical principles. * * * In this, as in many other cases, thefactcomes first, and takes us by surprise; after which we find that we had long been in possession of the principles from which it flowed, and that, with the clue we had in our hands, theory should have revealed the fact to us long before. M. Foucault’s communication describing his experiments is in theComptes Rendusof the Academy of Sciences, for 3rd February, 1851. His first experiments were made with a pendulum only two metres (6ft. 6¹⁄₄in.) in length, consisting of a steel wire from ⁶⁄₁₀ths to ¹¹⁄₁₀ths of a millimetre in diameter (the millimetre is the 25th part of an inch); to the lower end of which was attached a polished brass ball, weighing 5 kilogrammes, or 11 English pounds. * * * A metallicpoint projecting below the ball, and so directed as if it formed a continuation of the suspension wire, served as an index to mark the change of position more precisely. The pendulum hung from a steel plate in such a manner as to move freely in any vertical plane. To start the oscillatory movement without giving the ball any bias, it was drawn to one side with a cord, which held the ball by a loop; the cord was then burned, after which the loop fell off, and the vibrations (generally limited to an arc of 15 or 20 degrees) commenced. In one minute the ball had sensibly deviated from the original plane of vibration towards the observer’s left. Afterwards he experimented at the Observatory with a pendulum 11 metres (30 feet) long, and latterly at the Pantheon with one still longer. The advantage of a large pendulum, as compared with a small one, is, that a longer time elapses before it comes to a state of rest; for machinery cannot be employed here, as in a clock, to continue the motion. The pendulum is suspended over the centre of a circular table, whose circumference is divided into degrees and minutes. The vibrations are begun in the manner above described, and in a short time it is observed that the pendulum, instead of returning to the same point of the circle from which it started, has shifted to the left. Ifnarrowly observed, the change in the plane of vibration (says M. Foucault) is perceptible in one minute, and in half an hour, “Il saute aux yeux,” it is quite palpable. At Paris the change exceeds 11 degrees in an hour. Thus, supposing the oscillations to commence in a plane directed south and north, in two hours the oscillations will point SSW. and NNE.; in four hours they will point SW. and NE.; and in eight hours the oscillations will point due east and west, or at right angles to their original direction. To a spectator the change seems to be in the pendulum, which, without any visible cause, has shifted round a quarter of a circle; but the real change is in the table, which, resting on the Earth, and accompanying it in its rotation, has performed a fourth (and something more) of its diurnal revolution.

No one anticipated such a result; and the experiment has been received by some with incredulity, by all with wonderment; and one source of the incredulity arises from the difficulty of conceiving how, amidst the ten thousand experiments of which the pendulum has been the subject, so remarkable a fact could have escaped notice so long. Fully admitting that these experiments have generally been conducted with pendulums which had little freedom of motion horizontally, we still think odd thatsomebody did not stumble upon the curious fact.

Though all the parts of the Earth complete their revolution in the same space of time, it is found that the rate of horizontal motion in Foucault’s pendulum varies with the latitude of the place where the experiment is made. At the pole, the pendulum would pass over 15 degrees in an hour, like the Earth itself, and complete its circuit in 24 hours. At Edinburgh, the pendulum would pass over 12¹⁄₂ degrees in an hour, and would complete its revolution in 29 hours 7 minutes. At Paris, the rate of motion is 11 degrees and 20 minutes per hour, and the revolution should be completed in 32 hours.

Schematic representation of surfaceFIG. 31.

FIG. 31.

Let the above figure represent a portion of the Earth’s surface near the north pole N. Suppose the pendulum to be set in motion atm, so as to vibrate in the directionx y, which coincides with that of the meridianmN orm r. The Earth in the meantime is pursuing its easterly course, and the meridian linemN has come in six hours into the positionnN. It has been hitherto supposed that the pendulum would now vibrate in the new directionnN, assumed by the meridian, but thanks to M. Foucault, we now know that this is a mistake. The pendulum will vibrate in a planex n y, parallel to its original plane atm, as will be manifest if the plane of vibration points to some object in absolute space, such as a star. While the meridian linemN will in the course of 24 hours range round the whole circle of the heavens, and point successively in the directionnN,oN,pN,rN,sN,tN, anduN, the pendulum’s plane of vibrationx y, whether atm, atn, ato, atp, atr, ats, att, or atu, will always be parallel to itself, pointing invariably to the same star, and were a circular table placed under the pendulum, its plane of vibration, while really stationary, would appear to perform a complete revolution.

This stationary position of the plane of vibration at the pole seems to present littledifficulty. We impress a peculiar motion on the pendulum in setting it a going. The Earth is at the same time carrying the pendulum eastward, butat the polethe one motion will not interfere with the other. The only action of the Earth on the pendulum there is that of attracting it towards its own (the Earth’s) centre. But this attraction is exactly in the plane of vibration and merely tends to continue the oscillatory motion without disturbing it. It is otherwise if the experiment is made at some other point, say 20 degrees distant from the pole. Supposing the vibrations to commence in the plane of the meridian, then as the tendency of the pendulum is to continue its vibrations in planes absolutely parallel to the original plane, it will be seen, if we trace both motions, that, while it is carried eastward with the Earth along a parallel of latitude, this tendency will operate to draw the plane of vibration away from a ‘great circle’ into a ‘small circle’ (that is, from a circle dividing the globe into twoequalparts, into one dividing it into twounequalparts). But the pendulummustnecessarily move in a ‘great circle,’ and hence to counteract its tendency to deviate into a ‘small circle,’ a correctory movement is constantly going on, to which the lengthening of the period necessary to complete a revolution must be ascribed. At Edinburghthe period is about 29 hours, at Paris 32, at Cairo 48, at Calcutta 63. At the Equator, the period stretches out to infinity. M. Foucault’s rule is, that the angular space passed over by the pendulum at any latitude in a given time, is equal to the angular motion of the Earth in the period, multiplied by the sine of the latitude. The angular motion of the Earth is 15 degrees per hour; and at the latitude of 30, for example, the sine being to radius as 500 to 1000, the angular motion of the pendulum will consequently be 7¹⁄₂ degrees per hour. It is, therefore, easily found. It follows that the motions of the pendulum may be employed in a rough way to indicate the latitude of a place.”[37]

[37]Supplement of theManchester Examiner, of May 24, 1851.

Notwithstanding the apparent certainty of these pendulum experiments, and the supposed exactitude of the conclusions deducible therefrom, many of the same school of philosophy differed with each other, remained dissatisfied, and raised very serious objections both to the value of the experiments themselves, and to the supposed proof which they furnished of the Earth’s rotation. One writer in theTimesnewspaper of the period, who signs himself “B. A. C.,” says, “I have read the accounts of the Parisian experiment as they have appeared in many of our papers, and must confess that Istill remain unconvinced of the reality of the phenomenon. It appears to me that, except at the pole where the point of suspension is immovable, no result can be obtained. In other cases the shifting of the direction of passage through the lowest point that takes place during an excursion of the pendulum, from that point in one direction and its return to it again, will be exactly compensated by the corresponding shifting in the contrary direction during the pendulum’s excursion on the opposite side. Take a particular case. Suppose the pendulum in any latitude to be set oscillating in the meridian plane, and to be started from the vertical towards the south. It is obvious that the wire by which it is suspendeddoes not continue to describe a plane, but a species of conoidal surface; that when the pendulum has reached its extreme point its direction is to the south-west, and that as the tangent plane to the described surface through the point of suspension necessarily contains the normal to the Earth at the same point, the pendulum on its return passes through the same point in the direction north-east. Now, starting again from this point, we have exactly the circumstances of the last case, the primary plane being shifted slightly out of the meridian; when, therefore, the pendulum has reached its extreme point of excursion thedirection of the wire is to the west of this plane, and when it returns to the vertical the direction of passage through the lowest point is as much to the west of this plane as it was in the former case to the west of the meridian plane; but since it is now moving from north to south instead of from south to north, as in the former case, its former deviation receives complete compensation, and the primary plane returns again to the meridian, when the whole process recurs.”

In theLiverpool Mercuryof May 23, 1851, the following letter appeared:—“The supposed manifestation of the Rotation of the Earth.—The French, English, and European continental journals have given publicity to an experiment made in Paris with a pendulum; which experiment is said to have had the same results when made elsewhere. To the facts set forth no contradiction has been given, and it is therefore to be hoped that they are true. The correctness of the inferences drawn from the facts is another matter. The first position of these theorists is, that in a complete vacuum beyond the sphere of the Earth’s atmosphere, a pendulum will continue to oscillate in one and the same original plane. On that supposition their whole theory is founded. In making this supposition the fact is overlooked that thereis no vibratory motionunless through atmospheric resistance, or by force opposing impulse. Perpetual progress in rectilinear motion may be imagined, as in the corpuscular theory of light; circular motion may also be found in the planetary systems; and parabolic and hyperbolic motions in those of comets; but vibration is artificial and of limited duration. No body in nature returns the same road it went, unless artificially constrained to do so. The supposition of a permanent vibratory motion such as is presumed in the theory advanced, isunfounded in fact, and absurd in idea; and the whole affair of this proclaimed discovery falls to the ground. It is what the French call a ‘mystification’—anglice a ‘humbug.’ Liverpool, 22nd May, 1851.”“T.”

Another writer declared that he and others had made many experiments and had discovered that the plane of vibration had nothing whatever to do with the meridian longitude nor with the Earth’s motion, but followed the plane of the magnetic meridian.

“A scientific gentleman in Dundee recently tried the pendulum experiment, and he says—‘that the pendulum is capable of showing the Earth’s motion I regard as agross delusion; but that it tends to themagnetic meridianI have found to be a fact.’”[38]

[38]Liverpool Journal, May 17, 1851.

In many cases the experiments have not shown a change at all in the plane of oscillation of the pendulum; in others the alteration in the plane of vibration has been in thewrong direction; and very often therate of variationhas been altogether different to that which theory indicated. The following is a case in illustration:—“On Wednesday evening the Rev. H. H. Jones, F.R.A.S., exhibited the apparatus of Foucault to illustrate the diurnal rotation of the Earth, in the Library Hall of the Manchester Athenæum. The preparations were simple. A circle of chalk was drawn in the centre of the floor, immediately under the arched skylight. The circle was exactly 360 inches in its circumference, every inch being intended to represent one degree. According to a calculation Mr. Jones had made, and which he produced at the Philosophical Society six weeks ago, the plane of oscillation of the pendulum would, at Manchester, diverge about one degree in five minutes, or perhaps a very little less. He therefore drew this circle exactly 360 inches round, and marked the inches on its circumference. The pendulum was hung from the skylight immediately over the centre of the circle, the point of suspension being 25 feet high. At that length of wire, it should require 2¹⁄₂ seconds to make each oscillation across the circle. The brazen ball, which at the end of afine wire constituted the pendulum, was furnished with a point, to enable the spectator to observe the more easily its course. A long line was drawn through the diameter of the circle, due north and south, and the pendulum started so as to swing exactly along this line; to the westward of which, at intervals of three inches at the circumference, two other lines were drawn, passing through the centre. According to the theory, the pendulum should diverge from its original line towards the west, at the rate of one inch or degree in five minutes. This, however, Mr. Jones explained, was a perfection of accuracy only attainable in a vacuum, and rarely could be approached where the pendulum had to pass through an atmosphere subject to disturbances; besides, it was difficult to avoid giving it some slight lateral bias at starting. In order to obviate this as much as possible, the steel wire was as fine as would bear the weight, ¹⁄₃₀th of an inch thick; and the point of suspension was adjusted with delicate nicety. An iron bolt was screwed into the frame-work of the skylight; into it a brass nut was inserted—the wire passed through the nut (the hollow sides of which were bell-shaped, in order to give it fair play), and at the top the wire ended in a globular piece, there being also a fine screw to keep it from slipping. * * * The pendulum was gently drawn up to one side, at the southern endof the diametrical line, and attached by a thread to something near. When it hung quite still the thread was burnt asunder, and the pendulum began to oscillate to and fro across the circle. * * * Before it had been going on quite seven minutes, it had reached nearly the third degree towards the west, whereas itoughtto have occupied a quarter of an hour in getting thus far from its starting line, even making no allowance for the resistance of the atmosphere.”[39]

[39]“Manchester Examiner” (Supplement), May 24, 1851.

Besides the irregularities so often observed in the time and direction of the pendulum vibrations, and which are quite sufficient to render them worthless as evidence of the Earth’s motion, the use which the Newtonian astronomers made of the general fact that the plane of oscillation is variable, was most unfair and illogical. It was proclaimed to the world as a visible proof of the Earth’s diurnal motion; but the motion wasassumed to exist, and then employed to explain the cause of the fact which was first called a proof of the thing assumed! A greater violation of the laws of investigation was never perpetrated! The whole subject as developed and applied by the theoretical philosophers is to the fullest degree unreasonable and absurd—not a “jot or tittle” better than the reasoning contained in the following letter:—“Sir,—Allow me to call yourserious and polite attention to the extraordinary phenomenon, demonstrating the rotation of the Earth, which I at this present moment experience, and you yourself or anybody else, I have not the slightest doubt, would be satisfied of, under similar circumstances. Some sceptical and obstinate individuals may doubt that the Earth’s motion is visible, but I say from personal observation its a positive fact. I don’t care about latitude or longitude, or a vibratory pendulum revolving round the sine of a tangent on a spherical surface, nor axes, nor apsides, nor anything of the sort. That is all rubbish. All I know is, I see the ceiling of this coffee-room going round. I perceive this distinctly with the naked eye—only my sight has been sharpened by a slight stimulant. I write after my sixth go of brandy-and-water, whereof witness my hand,”—“Swiggins”—Goose and Gridiron, May 5, 1851.—“P.S. Why do two waiters come when I only call one?”[40]

[40]“Punch,” May 10, 1851.

The whole matter as handled by the astronomical theorists is fully deserving of the ridicule implied in the above quotation fromPunch; but because great ingenuity has been shewn, and much thought and devotion manifested in connection with it, and the general public thereby greatly deceived, it is necessary that the subjectshould be fairly and seriously examined. What are the facts?

First.—When a pendulum, constructed according to the plan of M. Foucault, is allowed to vibrate, its plane of vibration is often variable—not always. The variation when itdoesoccur, isnot uniform—is not always the same in the same place; nor always the same either in its rate or velocity, or in its direction. It cannot therefore be taken as evidence; for that which is inconstant cannot be used in favour of or against any given proposition. It thereforeis not evidence and proves nothing!

Secondly.—If the plane of vibrationisobserved to change, where is the connection between such change and the supposed motion of the Earth? What principle of reasoning guides the experimenter to the conclusion that it is the Earth which moves underneath the pendulum, and not the pendulum which moves over the Earth? What logical right or necessity forces one conclusion in preference to the other?

Thirdly.—Why was not the peculiar arrangement of the point of suspension of the pendulum specially considered, in regard to its possible influence upon the plane of oscillation? Was it not known, or was it overlooked, or was it, in the climax of theoretical revelry, ignored that a “ball-and-socket” joint is one which facilitatescircularmotion more readily than any other? and that a pendulum so suspended (as was M. Foucault’s), could not, after passing over one arc of vibration, return through the same arc without there being many chances to one that its globular point of suspension would slightly turn or twist in its bed, and therefore give to the return or backward oscillation a slight change of direction? Let theimmediate causeof the pendulum’s liability to change its plane of vibration be traced; and it will be found not to have the slightest connection with the motion or non-motion of the surface over which it vibrates.

At a recent meeting of the French Academy of sciences, “M. Dehaut sent in a note, stating that M. Foucault (whose experiments on the pendulum effected a few years ago at the Pantheon, are of European notoriety) is not the first discoverer of the fact that the plane of oscillation of the free pendulum is invariable; but that the honour of the discovery is due to Poinsinet de Sivry, who, in 1782, stated, in a note to his translation of ‘Pliny,’ that a mariner’s compass might be constructed without a magnet, by making a pendulum and setting it in motion in a given direction; because, provided the motion were continually kept up, the pendulum would continue to oscillate in the same direction, no matter by how many points, or how often the ship might happen to change her course.”

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