[2.]And, in one instance at least, of Asia also; for The Spy was translated into Persian! [Back to text]
[3.] 'The Prose-Writers of America.' [Back to text]
[WHY DOES THE PENDULUM SWING?]
The attention of the visitor to the recent Exhibition in Hyde Park was arrested, as he advanced westwards down the central promenade of the building, by a large clock busily at work marking off the seconds of passing time. That piece of mechanism had a remarkably independent and honest look of its own. The inmost recesses of its breast were freely bared to the inspection of every passer-by. As if aware of the importance of the work intrusted to its care, it went on telling, in the midst of the ever-changing and bustling crowd, with a bold and unhesitating click, the simple fact it knew; and that there might be no mistake, it registered what it told in palpable signs transmitted through the features of its own stolid face. Mr Dent's great clock was by no means the least distinguished object in the collection of the world's notabilities.
But there was one thing which nearly concerned that industrious and trusty monitor that he surely could not have known, or his quiet countenance would have shewn traces of perturbation. He was doing Exhibition work, but he was not keeping Exhibition time. The wonderful building in which he had taken up his temporary residence was, in fact, of too cosmopolitan a nature to have a time of its own. Its entire length measured off very nearly 1-42,000th part of the circle of terrestrial latitude along which it stretched. The meridian of the Liverpool Model was close upon thirty seconds of space farther west than the meridian of the Greek Slave. Imagine the surface of Hyde Park to have been marked off, before Messrs Fox and Henderson's workmen commenced their labours, by lines running north and south at the equal distance of a second of a degree from each other, just as one sees the surface of large maps traced by meridians, nearly thirty of those lines would then have been covered in by the east and west span of the crystal roof. Mr Dent's clock might have been set to the precise time of the Greek Slave, and it would yet have been nearly two seconds wrong by the time of the Liverpool Model. The pendulum swinging so steadily within its case had a longer and more stately stride than most of its congeners. It took a second and a half of time to complete its step from side to side. But notwithstanding this, if a string had been suddenly stretched across in space above the east end of the building, and left there in free suspension, independent of all connection with the terrestrial surface, it would have taken longer for the huge structure to be trailed beneath it by the earth's rotation—swift as that rotation is—than it did for the sober and leisurely mass of metal to finish its beat from side to side.
Our immediate business, however, at this present time is not with the geographical relations of Mr Paxton's building, but rather with that sober and leisurely-moving mass—the pendulum. Even in the seventeenth century, old Graunt was shocked when some irreverent babbler spoke of one of its honourable race by the rude epithet of 'a swing-swang;' and he penned an indignant protest on the subject to the Royal Society. Since that time the pendulum has done much more to merit the reverence of the world. Plain and simple as its outward bearing is, it really holds a high and dignified position in the annals of science.
Instead, however, of touching upon its pedigree and achievements, we proceed at once to speak of certain interesting peculiarities that enter as an element into all considerations in which it has concern. In the first place, what is that characteristic motion which it so constantly assumes—that restless swinging from side to side? Is it a property inherent in its own nature, or is it a power communicated to it from without? There is a train of wheelwork enclosed with it in the case. Is that the source of its vibratile mobility? Assuredly not. For if we arrest its motion with our hand at the instant that its form hangs perpendicularly suspended, that motion is not renewed although the wheels remain in unaltered relation. Those mechanical contrivances clearly do not comprise the secret of its swinging. We must look elsewhere if we would ascertain the fundamental cause.
Has the reader ever looked at the plain white building, with successive rows of little windows, which so often spans the breadth of our smaller streams? If he has, the thought has at once arisen that within those walls huge wheels and heavy-revolving stones remorselessly tear and crush to powder heaps upon heaps of yellow grain, with a power that is equal to the combined effort of a whole troop of horses concentred in the task. But we question very much whether he has as clearly seen whence those clattering wheels derive their many horse-power! If we were to ask him to tell us how they acquired their rolling strength, he would most probably answer—from the current of the stream. This reply would amount to nothing in the matter of explanation; the force of the current is as much a borrowed attribute as the force of the wheelwork. The running water is no more an independent and living agent than is the machinery which it turns. Beyond both is the one grand determining influence—the attractive energy inherent in the substance of the vast earth. This it is which makes the water run; this it is which enables the running water to move the wheelwork inserted into its channel. As the magnet draws to itself the fragment of steel, the earth draws to itself all ponderable matter; and whenever ponderable matter is free to move, it rushes as far as it can go towards the centre of the earth's substance, in obedience to the summons. Mobile water runs down from a higher to a lower level because the latter is nearer to the earth's centre than the former, and as it falls it pushes before it such minor obstructions as are unable to resist the influence of its weight. The float-boards of the mill-wheel are of this nature; they are striving to uphold the water by means of the rubbing and friction of the apparatus that is mechanically connected with the axle. But the resistance of the friction is less than the strength with which the earth tugs at the water, and therefore the wheel goes round and the water rushes down. The force which really grinds the hard corn into flour it terrestrial attraction! Gravitation of material substance towards material substance, acting with an energy proportioned to the relative masses and to the relative distances of the elements concerned.