POPULAR MISCELLANY. 



717 



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. 



The Medium 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 takes 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. 

 If 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 



