174 



WRITINGS OF JOSEPH HENRY. [1855- 



nitrate of ammonia. To the atmosphere is also probably due 

 the nitric acid which forms the nitrate of lime, from which the 

 nitrate of potash, the principal ingredient of gunpowder, is 

 produced in the soil containing the base. We have in this 

 instance another confirmation of the conservation and trans- 

 formation of power. The discharge of the electricity in the 

 heavens expends a portion of its energ}^ in producing a change 

 in the condition of oxygen which in its turn attracts and 

 imprisons (as it were) a portion of nitrogen — a substance 

 which of all others, appears to possess the greatest repulsive 

 energy, and the violent breaking loose again of this from its 

 combination exhibits its power in the explosion which ensues. 

 In this way the bolt of Jove may be said to be partly trans- 

 formed into that of Mars, and the thunder of war to be but 

 a reverberation of that of the heavens. 



Odors. — The observations which have been made during 

 the photographic process have revealed the fact of the exis- 

 tence in the air of the vapors of metals and other substances 

 which though so minute as to have escaped particular 

 attention are yet sufficient to interfere materially with the 

 operations necessary to the production of perfect pictures. 

 Almost all metals heated to redness give off effluvia percep- 

 tible by the sense of smell. 



The diffusion in the air of the odoriferous principle 

 of plants and other substances is a subject worthy of more 

 attention than it has yet received. The wide diffusion 

 of an almost infinitesimal quantity of matter in these cases 

 may well excite our astonishment. A single grain of musk 

 has been known to scent a room for twenty years, and 

 without apparent reduction of the original material. To 

 produce this result, the minuteness of the atoms must be 

 beyond the conception of the imagination. From the in- 

 fluence which chlorine has upon animal and vegetable odors, 

 it is probable that hydrogen is an essential part of their com- 

 position. The atmosphere itself, when pure, is inodorous; 

 but the absence of perceptible odor may be due to the fact 

 that our sense of smell ceases in some cases to indicate an 

 odor after having been for a certain time subjected to its in- 



