Page:Popular Science Monthly Volume 12.djvu/126

116 but this he shows to be impracticable; the other method is to use part of the power of the engine to pump back the discharged steam, containing as it does some water condensed from the steam, into the boiler. This latter method is theoretically practical, and the purely mechanical difficulties in the way of its realization are by no means insuperable.

As the steam in the cylinder of an engine expands, doing work, part of it condenses. The difference between the heat-energy of the steam at the beginning of the stroke, and that of the steam and water at the end of the stroke, is equal to the heat-equivalent of the mechanical work done by the steam. The change of mechanical condition which the steam undergoes during the stroke—namely, its conversion into water—renders it possible that the mingled steam and water remaining in the cylinder at the end of the stroke may be forced back into the boiler with a less expenditure of mechanical energy than the steam gave out during the stroke.

The Telephone anticipated.—As is the case with all great inventions, the telephone is now said to be nothing new; its principle was known long ago, and even exemplified in practice. Many are the claimants of priority in solving the problem of the transmission of articulate sound to great distances, but we know of none whose case is stronger than that of "Monsieur Ch. B," who appears to have solved the problem as early as 1857. In the Count du Moncel’s "Exposé des Applications de l'Électricité," published twenty years ago, occurs the following passage (translated in Nature):

"After the marvelous telegraphs which are able to reproduce at a distance writing of this or that individual, and designs more or less complicated, it seemed impossible, said M. B, to advance further in the regions of the marvelous. Nevertheless, essaying to do something more, I asked, for example, if speech itself would not be capable of transmission by electricity; in a word, if one would not be able to speak at Vienna and be heard at Paris. The thing is practicable. This is how: Sounds, it is known, are formed by vibrations and carried to the car by these same vibrations, which are reproduced by the intermediate media. But the intensity of these vibrations diminishes very rapidly with the distance, from which it follows, even in the employment of speaking-trumpets, tubes, and of acoustical horns, the limits which cannot be surpassed are very restricted. ''Imagine that one speaks near a mobile plate, flexible enough not to lose any of the vibrations produced by the voice; that this plate establishes and interrupts successively the communication with a battery. You would be able to have at a distance another plate which would execute at the same time the same vibrations. It is true that the intensity of the sounds produced would be variable at the point of departure, where the plate is vibrated by the voice, and constant at the point of arrival, where it is vibrated by electricity.'' But it is demonstrable that this would not alter the sounds. . . . In any case, it is impossible to demonstrate that the electric transmission of sounds is impossible. . . . An electric battery, two vibrating plates, and a metallic wire, will suffice."

The Slaves of Ants.—The subjugation of other insects by various species of ants is a familiar fact of natural history; it is less usual to see two or more species thus subjugated. Prof. Leidy, in some remarks made at a meeting of the Academy of Natural Science of Philadelphia, recounts his observations on a colony of yellow ants (Formica flava), which had three different insects in their service, namely, a species of Aphis, a Coccus, and the larva of an insect, probably coleopterous. The aphides, he tells us, were kept in two separate herds, and these were separated from a herd of cocci. The larva was in the midst of one of the former herds. In another and larger colony of yellow ants there was a herd of aphides which occupied the under-part of one margin of the stone under which the ants had their nest; the surface occupied by these aphides was about ten inches long: and three-fourths of an inch broad. The same colony also possessed a separate herd of cocci, closely crowded, and occupying almost a square inch of space. Both aphides and cocci, with few exceptions, adhered to the under-surface of the stone, and were not attached to the roots. They appeared to be carefully attended by the ants, which surrounded them. The larva, too, was carefully attended by the ants, which were frequently observed to stroke it with their antennae. The aphides and cocci were all in good condition, but without visible means of subsistence, excepting the neighboring grass-roots partially extending into the earth beneath the stones, to which they probably were at times transferred by their masters.