From the experiment described in Wheatstone’s paper (Philosophical Transactions for 1834), it would appear that the human eye is capable of perceiving phenomena of light whose duration is limited to the millionth part of a second.
In Professor Airy’s experiments with the electric telegraph to determine the difference of longitude between Greenwich and Brussels, the time spent by the electric current in passing from one observatory to the other (270 miles) was found to be 0·109″ or rather more than the ninth part of a second; and this determination rests on 2616 observations: a speed which would “girdle the globe” in ten seconds.
IDENTITY OF ELECTRIC AND MAGNETIC ATTRACTION.
This vague presentiment of the ancients has been verified in our own times. “When electrum (amber),” says Pliny, “is animated by friction and heat, it will attract bark and dry leaves precisely as the loadstone attracts iron.” The same words may be found in the literature of an Asiatic nation, and occur in a eulogium on the loadstone by the Chinese physicist Knopho, in the fourth century: “The magnet attracts iron as amber does the smallest grain of mustard-seed. It is like a breath of wind, which mysteriously penetrates through both, and communicates itself with the rapidity of an arrow.”
Humboldt observed with astonishment on the woody banks of the Orinoco, in the sports of the natives, that the excitement of electricity by friction was known to these savage races. Children may be seen to rub the dry, flat, and shining seeds or husks of a trailing plant until they are able to attract threads of cotton and pieces of bamboo-cane. What a chasm divides the electric pastime of these naked copper-coloured Indians from the discovery of a metallic conductor discharging its electric shocks, or a pile formed of many chemically-decomposing substances, or a light-engendering magnetic apparatus! In such a chasm lie buried thousands of years, that compose the history of the intellectual development of mankind.—Humboldt’s Cosmos, vol. i.
THEORY OF THE ELECTRO-MAGNETIC ENGINE.
Several years ago a speculative American set the industrial world of Europe in excitement by this proposition. The Magneto-Electric Machines often made use of in the case of rheumatic disorders are well known. By imparting a swift rotation to the magnet of such a machine, we obtain powerful currents of electricity. If these be conducted through water, the latter will be reduced to its two components, oxygen and hydrogen. By the combustion of hydrogen water is again generated. If this combustion takes place, not in atmospheric air, in which oxygen only constitutes a fifth part, but in pure oxygen, and if a bit of chalk be placed in the flame, the chalk will be raised to a white heat, and give us the sun-like Drummond light: at the same time the flame develops a considerable quantity of heat. Now the American inventor proposed to utilise in this way the gases obtained from electrolytic decomposition; and asserted that by the combustion a sufficient amount of heat was generated to keep a small steam-engine in action, which again drove his magneto-electric machine, decomposed the water, and thus continually prepared its own fuel. This would certainly have been the most splendid of all discoveries,—a perpetual motion which, besides the force that kept it going, generated light like the sun, and warmed all around it. The affair, however, failed, as was predicted by those acquainted with the physical investigations which bear upon the subject.—Professor Helmholtz.
MAGNETIC CLOCK AND WATCH.
In the Museum of the Royal Society are two curiosities of the seventeenth century which are objects of much interest in association with the electric discoveries of our day. These are a Clock, described by the Count Malagatti (who accompanied Cosmo III., Grand Duke of Tuscany, to inspect the Museum in 1669) as more worthy of observation than all the other objects in the cabinet. Its “movements are derived from the vicinity of a loadstone, and it is so adjusted as to discover the distance of countries at sea by the longitude.” The analogy between this clock and the electric clock of the present day is very remarkable. Of kindred interest is “Hook’s Magnetic Watch,” often alluded to in the Royal Society’s Journal-book of 1669 as “going slower or faster according to the greater or less distance of the loadstone, and so moving regularly in any posture.”