IO2 Hitman Physiology. 



vibrations of a space-filling elastic medium? Can the vibra- 

 tions of a substance, as much finer than air as that is finer than 

 granite, melt granite itself, and keep the whole Earth molten? 

 Yet it seems to be demonstrated that the light of the sun all 

 its rays, red, yellow, blue, and their combinations, heat rays, 

 actinic rays, are but the varied perturbations of a medium 

 filling all space, through which come the vibrations of stars so 

 distant that they are centuries in coming. What, then, is this 

 medium? Has it atoms, with their elastic forces of attraction 

 and repulsion ? We can conceive of no other kind and this 

 is past conception. 



In such an ether, with vibrations corresponding to every shade 

 of light and colour, there must be myriads of waves or impul- 

 sions in every second of time, transmitted at the rate of 3 7 5,000 

 miles in a second. These impulses pass through the most solid 

 substances, as glass and crystals. Crystals of salt allow the 

 passage of both light and heat. Seventy-five per cent of heat 

 is stopped by a plate of crown glass, but a second plate only 

 stops ten per cent, of heat which passed through the first. Blue 

 glass stops the red rays. Light passes freely where electricity 

 can find no passage. Light and heat are both reflected from 

 surfaces, as sounds are thrown back in echoes. Heat is also 

 radiated from all bodies, so that there is a constant tendency 

 to equilibrium. A convex lens brings the rays both of light 

 and heat to a focus, and, with a large glass, the hardest metals 

 may be melted by the vibrations caused by a body nearly a 

 hundred millions of miles distant. 



The sun, by its action upon the luminiferous ether which fills 

 the universe, keeps the Earth, and all planets, no doubt, at the 

 temperature required for vegetation and animal life. It is under 

 the action of light that vegetables decompose the carbonic acid 

 of the atmosphere. The light and heat of the sun raise the 

 water into the atmosphere that makes life possible upon the 

 earth. All force, all life, or the conditions of life, seem to come 



