Page:Popular Science Monthly Volume 20.djvu/150

140 its excess of heat by conductivity. The luminous and ultra-violet rays produce a similar effect; but the motion which they communicate to the molecules is distinguished by greater velocity, corresponding to a higher temperature. Such an hypothesis of molecular heating is sufficient to explain most of the effects produced by light on bodies. The incandescence of the superficial molecules, under the influence of the most refrangible rays emanating from a source at high temperature, must persist for a finite time after the cessation of the action of light. In this, perhaps, lies the direct explanation of the phosphorescence of short duration which M. Ed. Becquerel has observed in nearly all solid bodies. Fluorescence is also explained by the same hypothesis, if we regard it as a phosphorescence of short duration sufficiently intense to be seen during the action of the light. In general, moderate elevation of temperature favors the reactions of combination, while in the highest temperatures all known combinations undergo dissociation or decomposition. Thus, according to M. Lermantoff s hypothesis, the less refrangible parts of the spectrum should produce principally reactions of combination, and the more refrangible parts decompositions. This is precisely what M. Chastaing has proved for the particular case of oxidations.

Metallic Anti-Resonators.—It is known that resonances in public halls can be modified or prevented by stretching wires across the ceilings; and the principle has been rudely applied in a number of instances with fairly satisfactory results. Mr. A. C. Engler, of London, has invented a plan for a systematic arrangement of steel plates, or wires, which promises to accomplish the object more completely. The effect of the plates is to take up the most gentle vibrations and greatly to increase the speed of transmission. Wires have a similar property, and are more convenient. In the most advantageous application of Mr. Engler's invention, one or more layers of steel wires are stretched along the length of the room, a few feet below the ceiling, connected by cross-wires and spiral springs, and properly tuned, so that the vibration may be absorbed and conveyed from one wire to another, and instantaneously spread over the whole building; and the words of the speaker or the notes of the singer are so accelerated that they reach the audience about fifteen times more quickly than under ordinary arrangements. The effect is improved and the tone enriched by using steel plates. The system has been applied—imperfectly, for the wires had to stop short of the wall at one end in a lecture-room at the South Kensington Museum of notoriously bad acoustic properties. Twenty-eight lengths of steel wire were stretched across a distance of sixty feet, and connected at the end by steel-wire springs. Above them were three other steel wires, connected with the lower group, so as to form a perfect network of wires. The effect was a complete distribution of the sound, so that a speaker at the lecturer's table could be heard distinctly in any part of the theatre, and all the acoustic defects of the hall were considerably mitigated.

Decline of Country Population in England.—The returns of the new English census show that the growth of the towns at the expense of the rural villages and the agricultural districts, which has been remarked in previous censuses, still continues; and it is not certain that the process of depletion of the country is not progressive. The younger people are leaving their rural homes so rapidly that in some parts of the kingdom the difference is sufficient to strike even casual travelers. The causes of the decline of the agricultural population are supposed to be attributable partly to the increasing use of machinery, which reduces the demand for hands; partly to reduction of wages; but chiefly to an increase in the dislike for agricultural labor under existing conditions. The towns offer better pay, more steady employment, better protection from the weather, and more hope of reaching an improved condition, than the farms; and work in towns, if it is hard, is more lively and gregarious than agricultural labor. The remedy suggested for the evil, if one is to be applied, is peasant proprietorship, under which the man who works may, as on the Continent and in the United States, feel that he is laboring for himself.