284 INDEX. 



Hydrogen : combines with other substances and simple atoms as if it were 



a simple element, i. 106 



sulphuretted, amount of absorption of radiant heat by, i. 41 

 opacity of, to the invisible rays, i. 65 

 one of the illuminants in coal gas, i. 118 

 how freed from coal gas, i. 118 

 Hydrozoa, campanograde, characters of, ii. 103 

 ciliograde, characters of the, ii. 101 

 mode of reproduction of, ii. 103 

 oceanic, structure of, ii. 81, 86 

 compound oceanic, structure of, ii. 87 

 medusiform zooids, ii. 88, 89 

 mode of reproduction of, ii. 89, 90 

 Hymenocetes, family of, i. 261 

 Hymenophyllum, stem of, i. 339 



Hymenophyllumtunbridgense, orfilm fern, structure and habitat of, i. 362 

 Hymenophyllum unilaterale, habitat and structure of, i. 362 

 Hyphomycetes, characters of the family, i. 282 

 Hypogsei, structure and fructification of the subterranean sub-order of, 



i. 267, 268 



Hyponitrous acid, combination forming, i. 95 

 Hypopterygium Smithianum, leaves of, i. 330 



Ice, absorption of invisible rays by, i. 65 



believed to be a colloid body, i. Ill 

 Iceland moss, characters of, i. 304 

 Iceland spar, polarization of light and heat in, by refraction, i. 69 



change of position of the optical axes of the crystals of, by heat, 



i. 73 



Ileodictyon, eaten as food, i. 268 

 Impetus, i. 26, 27 



heat generated by, i. 27 



combustion a case of, i. 30 



Indian rubber, dissolved by naphtha for waterproofing, i. 120 

 Indium, discovery of the metal so called, i. 137 



properties of, i. 137 

 Infusoria, structure, form, and habitat of, ii. 63 



abundance of infusoria in the atmosphere, ii. 63, 64 



different states of development in one and the same animal, ii. 65 



