Page:Popular Science Monthly Volume 35.djvu/741
��the original constitution of the matter which was drawn together to form our planet. The character of all inorganic substances, as of all living creatures, is only consistent with the actual constitution and proportion of the various substances of which the earth is composed. Other proportions than those present in the constituents of the atmos- phere would have required a different organ- ization in all air - breathing animals, and probably in all plants. Any considerable difference in the quantity of water, either in the sea or distributed as vapor, must have involved corresponding changes in the con- stitution of living creatures.
Tbe Medinm of Electro-magnetic Action.
— It was decided by experiment, during 1888, according to Prof. G. F. Fitzgerald, in the British Association, that electro-magnetic action talies place, not at a distance, but through an intervening medium. The ex- periments were made by Hertz in Germany, who observed the interference of electro- magnetic waves quite analogous to those of light, and proved that electro-magnetic ac- tions are propagated in air with the velocity of light. " By a beautiful device Hertz has produced rapidly alternating currents of such frequency that their wave-length is only about two metres. I may pause for a min- ute to call your attention to what that means. K they vibrated three hundred thousand times a second, the waves would be each a kilometre long. This rate of vibration is much higher than the highest audible note, and yet the waves are much too long to be manageable. We want a vibration about a thousand times as fast again, with waves about a metre long. Hertz produced such vibrations, vibrating more than a hundred million times a second." While this rate is too slow for visibility or light, and the vi- brations are also inaudible, the experimenter was able to detect them by resonance. He constructed a circuit whose period of vibra- tion for electric currents was the same as that of his generating vibrator, and "was able to see sparks, due to the induced vibra- tion, leaping across a small air-space in this resonant circuit." By this combination — of a vibrating generating circuit with a resonant receiving circuit — which the author had rec- ommended at the Southport meeting of the
��Association to be used for this very investi- gation, Hertz was able to observe the inter- ference between waves incident on a wall and the reflected waves. The phenomenon is the same as what are known as Lloyd's bands, in optics, which are due to the inter- ference between a direct and a reflected wave. " It follows, hence, that just as Young's and Fresnel's researches on the interference of light prove the undulatory theory of optics, so Hertz's experiment proves the ethereal theory of electro-magnetism. It is a splen- did result. Henceforth I hope no learner will fail to be impressed with the theory — hypothesis no longer — that electro-magnetic actions are due to a medium pervading all space, and that it is the same medium as the one by which light is conducted."
Washing Men and Children by Machin- ery. — One of the latest inventions in sanita- tion is machinery for personal washing. A French colonel, according to Mr. Edwin Chad- wick, ascertained that he could wash his men with, tepid water for a centime, or one tenth of a penny a head, soap included. The man undresses, steps into a tray of water, and soaps himself, when a jet of tepid water is played upon him. He then dries and dresses himself in five minutes, against twenty min- utes in the bath, and with five gallons of water against seventy in the usual bath. In Ger- many they have an arrangement under which half a million of soldiers are regularly washed. By an adaptation of apparatus to the use of schools, a child may be completely washed in three minutes.
Modern Deterioration of Eye-sight. — Dr.
R. Brudenell Carter, when questioned about the causes of modern deterioration of eye- sight, replied that the circumstances of civili- zation are unfavorable to the cultivation of eye-sight. We are not as dependent on keen- ness of vision as our ancestors were. Much of the work of dwellers in towns is done upon objects close to them, from which they obtain large retinal images, whence they be- come comparatively insensible to small ones. They often work by defective light, and are thus driven to approach the object still more closely ; and it is by such approximation that the malformation which produces short sight is mainly brought about. The increase