282 INDEX. 



Heat : intensity of the heat of the electric spark, i. 32 

 proof of the correlation of heat and electricity, i. 33 

 constancy in the amount and refrangibility of the light and heat 



absorbed and radiated, i. 34 



property of some substances in the transmission of heat, i. 36 

 substances which transmit radiant heat freely but radiate badly, and 



vice versa, i. 37 

 Tyndall's experiments on the radiation and absorption of radiant 



heat by gases and vapours, i. 38 



relation between the density of the gas and the quantity of heat ex- 

 tinguished or absorbed, i. 40 



absorption of radiant heat by the vapours of volatile liquids, i. 40 

 Prof. Tyndall's experiments showing the radiation to be equal to 



the absorption of radiant heat, i. 46 

 action of different thicknesses of the same gas or vapour on radiant 



heat, i. 47 



dynamic absorption and radiation, i. 49 

 dynamical evolution of heat, i. 52 



experiment illustrating the change of heat into light, i. 62 

 polarization of heat and light, i. 68, 69 

 by reflection and refraction, i. 69 



effect of heat on the magnetism of iron, nickel, and cobalt, i. 77 

 extreme heat and light of electric discharges, i. 84 

 instances of the correlation of electricity and heat, i. 91 

 capacity of atoms for heat, i. 1 00 



Mr. Croll's experiments, i. 101 

 effects of heat on vegetation, i. 169 

 large amount of heat evolved by vegetables, i. 265 

 cause of animal heat, ii. 63 



Helix, or snail, tentacles of, ii. 236 



Helix aspera, structure of the tongue of, ii. 237 



Helix pomatia, teeth of, ii. 237 



Hellebore, white, poisonous alkaloid of, i. 427 



Helmet shell, structure of, ii. 234 



Helminthosporium Hoffmanni, spores of, i. 285, 286 



Helminthosporium nodosum, spores of, i. 286. 



Helvella, structure and habitat of, i. 291 



Hepaticze, or liverworts, characters of the, i. 316 



Hepialus virescens of New Zealand, Cordyceps Robertsii of the, i. 293 



Hersehel, Sir W., his discovery of invisible rays of light of high heating 

 power, i. 36 



Hewardia, structure of, i. 359 



