Inflection 

 Lelics 



SCIENTIFIC SIDE-LIGHTS 



578 



light is decomposed, quitting the drop re- 

 solved into colored constituents. The light 

 thus reaches the eye of an observer facing 

 the drop, and with his back to the sun. 

 TYNDALL Lectures on Light, lect. 1, p. 24. 

 (A., 1898.) 



2853. REFRACTION, DOUBLE, OF 

 LIGHT Iceland Spar. Pour water and di- 

 sulfid of carbon into two cups of the same 

 depth; the cup that contains the more 

 strongly refracting liquid will appear shal- 

 lower than the other. Place a piece of Ice- 

 land spar over a dot of ink; two dots are 

 seen, the one appearing nearer than the 

 other to the eye. The nearest dot belongs 

 to the most strongly refracted [the ordi- 

 nary] ray, exactly as the nearest cup bottom 

 belongs to the most highly refracting liquid. 

 When you turn the spar round, the extraor- 

 dinary image of the dot rotates round the 

 ordinary one, which remains fixed. TYNDALL 

 Lectures on Light, lect. 3, p. 114. (A., 

 1898.) 



2854. REFRACTION ENHANCES 

 SENSE OF VASTNESS Steppes of South 

 America. The distant aspect of the steppe 

 is the more striking when the traveler 

 emerges from dense forests, where his eye 

 has been familiarized to a limited prospect 

 and luxuriant natural scenery. I shall ever 

 retain an indelible impression of the effect 

 produced on my mind by the llanos, when, 

 on our return from the Upper Orinoco, 

 they first broke on our view from a distant 

 mountain, opposite the mouth of the Rio 

 Apure, near the Hato del Capuchino. The 

 last rays of the setting sun illumined the 

 steppe, which seemed to swell before us like 

 some vast hemisphere, while the rising stars 

 were refracted by the lower stratum of the 

 atmosphere. When the plain has been ex- 

 cessively heated by the vertical rays of the 

 sun, the evolution of the radiating heat, 

 the ascent of currents of air, and the con- 

 tact of atmospheric strata of unequal den- 

 sity continue throughout the night. HUM- 

 BOLDT Views of Nature, p. 28. (Bell, 1896.) 



2855. REFRACTION OF LIGHT 



Diminished Velocity in Denser Medium, as 

 Glass or Water. According to the undula- 

 tory theory, the velocity of light in water 

 and glass is less than in air. Consider, then, 

 a small portion of a wave issuing from a 

 point of light so distant that the portion 

 may be regarded as practically plane. Mov- 

 ing vertically downwards, and impinging on 

 an horizontal surface of glass or water, the 

 wave would go through the medium with- 

 out change of direction. But as the velocity 

 in glass and water is less than the velocity 

 in air, the wave would be retarded on pass- 

 ing into the denser medium. But suppose 

 the wave, before reaching the glass, to be 

 oblique to the surface, that end of the wave 

 which first reaches the medium will be the 

 first retarded by it, the other portions as 



they enter the glass being retarded in suc- 

 cession. It is easy to see that this re- 

 tardation of the one end of the wave must 

 cause it to swing round and change its front, 

 so that when the wave has fully entered the 

 glass its course is oblique to its original 

 direction. According to the undulatory 

 theory, light is thus refracted. TYNDALL 

 Lectures on Light, lect. 3, p. 109. (A., 

 1898.) 



2856. REFRIGERATION BY EX- 

 PANSION Liquefaction of Oxygen, Nitrogen, 

 Hydrogen, and Air. In 1877 M. Cailletet 

 had liquefied nitric oxid and acetylene, and 

 on the 2d of December he placed in the 

 hands of M, Henri Saint-Claire Deville a 

 note wherein, in cautious but distinct terms, 

 he announced the liquefaction of oxygen. 

 On the 16th of the same month he repeated 

 his experiments. . . . His plan of oper- 

 ation involved the application of the prin- 

 ciple of refrigeration by expansion. . . . 

 By instruments of great strength and su- 

 preme accuracy of fit he was able to sub- 

 ject a volume of oxygen gas to a pressure 

 of 300 atmospheres. He might have mul- 

 tiplied this pressure tenfold without lique- 

 fying the gas, but instead of augmenting 

 the pressure he suddenly released the gas 

 from the pressure imposed upon it. It for- 

 cibly expanded, and the cold of expansion 

 caused the gas to precipitate itself as a 

 cloud, which the eminent men who witnessed 

 the experiment agreed in pronouncing liquid 

 oxygen. He subsequently applied the same 

 method with success to nitrogen, hydrogen, 

 and air, all of which, through the combina- 

 tion of pressure with sudden release from 

 pressure, were caused to precipitate them- 

 selves in clouds. TYNDALL Heat a Mode of 

 Motion, lect. 5, p. 145. (A., 1900.) 



2857. REGELATION, FARADAY'S 

 DISCOVERY OF Blocks of Ice Freeze To- 

 gether under Hot Water. In a lecture given 

 at the Royal Institution in June, 1850, and 

 reported in the Athenceum and Literary Ga- 

 zette for that year, Faraday showed that 

 when two pieces of ice, at a temperature of 

 32 F., are placed in contact with each 

 other they freeze together by the conversion 

 of the film of moisture between them into 

 ice. The case of a snowball is a familiar 

 illustration of the principle. When the 

 snow is below 32, and therefore dry, it 

 will not cohere, whereas when it is in a 

 thawing condition it can be squeezed into a 

 hard mass. During one of the hottest days 

 of July, 1857, when the thermometer was 

 upwards of 100 F. in the sun, and more 

 than 80 in the shade, I observed a num- 

 ber of blocks of ice, which had been placed 

 in a heap, frozen together at their places of 

 contact, and I afterwards caused them to 

 freeze together under water as hot as the 

 hand could bear. TYNDALL Hours of Exer- 

 cise in the Alps, ch. 1, p. 354. (A., 1898.) 



