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 was assumed 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 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 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 from Punch; 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 subject should 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 it does occur, is not 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 therefore is not evidence and proves nothing!
Secondly.—If the plane of vibration is observed 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 facilitates circular motion 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 the immediate cause of 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.”
SECTION 13.
PERSPECTIVE ON THE SEA.
It has been shown (at [pages 25] to [34]) that the law of perspective, as commonly taught in our Schools of Art, is fallacious and contrary to everything seen in nature. If an object be held up in the air, and gradually carried away from an observer who maintains his position, it is true that all its parts will converge to one and the same point; but if the same object be placed upon the ground and similarly moved away from a fixed observer, the same predicate is false. In the first case the centre of the object is the datum to which every point of the exterior converges; but in the second case the ground becomes the datum, in and towards which every part of the object converges in succession, beginning with the lowest, or that nearest to it.
Instances:—A man with light trousers and black boots walking along a level path, will appear at a certain distance as though the boots had been removed, and the trousers brought in contact with the ground.