In the Liverpool Mercury of May 23, 1851, the following letter appeared:
"SIR,--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 there is no vibratory motion unless 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, is unfounded in fact and absurd in idea; and the whole affair of this proclaimed discovery falls to the ground.
"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.
The Liverpool Mercury, of May 17th, 1851, contains the following
"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 a gross delusion; but that, it tends to the magnetic meridian I have found to be a fact.'"
In many cases the experiments have not shown a change at all in the plane of oscillation of the pendulum; in others the alteration has been in the wrong direction, and very often the rate of variation has been altogether different--too fast or too slow--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 to 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 2½ seconds to make each oscillation across the circle. The brazen ball, which at the end of a fine 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 framework 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 end of 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 it ought to 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." 1
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 is true that the advocates of a globular and revolving world had no single fact or experiment which they could point to as proof of their theory, and "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 planetary motions 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." 1
This acknowledged absence of any "direct proof'' of the earth's rotation evidently created a premature rejoicing when it was announced from Paris that at length an experiment had been hit upon which would render it "palpable to the senses." A trumpet-tone proclaimed to the scientific world that at length, after centuries of groping speculation, a visible proof of the earth's diurnal motion had been discovered; that what had remained for generations a pure assumption, was now found to be a mechanical fact. It was obtruded and commented upon--never logically discussed, in every journal, both scientific and literary, as well as merely miscellaneous, in almost every part of the world. The pride and exultation of astronomers became almost unbounded, and heedless of restraint. But after a time their clamorous triumph over all who had doubted the truthfulness of the Newtonian system suddenly ceased. The blinding meteor had fallen into the sea and become extinguished. A deceptive theory had allured them into a morass of false and illogical reasoning. They had long before assumed that the earth had diurnal rotation; and now, instead of admitting the simple fact that the pendulum, under certain conditions, did not maintain its original plane of vibration, they again, contrary to every principle of justice and reason, recklessly dared to assume that it was not the pendulum at all, but the earth underneath it which "parted company," and moved away to the west.
The motion of the earth was first assumed to exist; and when there still was no visible sign of motion, they again assumed that their first assumption was right, and affirmed that that which really and visibly moved could not be moving, because that which could not be seen or proved to move must be in motion according to their theory or first assumption! The pendulum, as though a living creature, conscious of unbearable defamation, subsequently became so irregular in its behaviour that the astronomers did and were glad to disown it as an ally or friend of their calumnious philosophy. They struggled fiercely to retain its peculiarities as a proof of their groundless assumptions, but the battle was short and decisive. The pendulum ignored the connection; and the scientific world was compelled to submit to a divorce, and to acknowledge defeat. Their reasoning had been dexterous, but false and devious. A greater violation of the laws of investigation was never perpetrated. The whole subject, as developed and applied by the theoretical philosophers, was to the fullest degree unreasonable and absurd--not a "jot or tittle" better than the "reasoning" contained in the following letter:--
"TO THE EDITOR OF 'PUNCH.'
"SIR,--Allow me to call your serious 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 it's a positive fact.
[paragraph continues] 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?" 1
The whole matter, as handled by the astronomical theorists, is fully deserving of the ridicule implied in the above quotation. But because great ingenuity and much thought and devotion have been manifested in connection with it, and the general public thereby greatly deceived, it is necessary that the subject should be fairly and seriously examined. What are the facts as developed by numerous, and often-repeated experiments?
FIRSTLY,--When a pendulum, constructed according to plan of M. Foucault is allowed to vibrate, its plane of the vibration is often stationary and often variable. The variation is not uniform--is not always the same in the same place; nor the same in its rate, or velocity, or in its direction. This great variability in its behaviour is not compatible with the assumption of an earth or world globular in form and moving with uniform velocity. It cannot therefore be taken as evidence; for that which is inconstant is inadmissible, and not to be relied on. Hence it is not evidence, and nothing is proved or decided by its consideration.
SECONDLY.--Admitting the plane of vibration as changeable, 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 on the plane of oscillation? Was it not known, or was it overlooked, or was it, in the climax of theoretical revelry, ignored--thought unworthy of consideration--that a "ball-and-socket" joint, or a globular point of suspension on a plane surface, is one which facilitates circular motion more readily than any other, and that a pendulum so suspended (as M. Foucault's) could not, after passing over one arc of vibration, return through the same arc without many chances to one that its globular point of suspension would slightly turn or twist on its bed, and therefore give to the return or backward oscillation a slight change of direction? Changes in the electric and magnetic conditions of the atmosphere, as well as alterations in its density, temperature, and hygrometric state may all tend in addition to the peculiar mode of suspension, to make the pendulum oscillate in irregular directions. So far, then, as we have been able to trace the subject, we are compelled by the evidence obtained to deny that the variations observed in the oscillations of a freely vibrating pendulum have any connection whatever with
the motion or non-motion of the surface over which it vibrates.
307:1 "Manchester Examiner," supplement, May 24, 1851.
308:1 "The Scotsman," a scientific article, by the editor, Mr. Charles Maclaren.
310:1 "Punch," May 10, 1851.