THE STORAGE OF COLD. 517 



THE STORAGE OF COLD. 



By chaeles moeeis. 



THERE are two processes constantly active upon the surface 

 of the earth which are of the utmost importance as regards 

 its suitability for human habitation the storage of heat and the 

 storage of cold. Of these we are here concerned only with the lat- 

 ter. The source and method of the storage of cold (a negative 

 process, which we may here treat as a positive) are much less evi- 

 dent and not so generally known as those of heat-storage, and a 

 review of them may be of interest. 



The source of the stored cold is the upper atmosphere, and the 

 principal storing substance snow. Here we are on ground famil- 

 iar only to scientists. Readers generally are not aware of the 

 vitally important part which snow plays in the economy of 

 nature. The lightly falling snow-flake, with its poetic affiliation 

 and its attractive aspects, has its aspect of terror as well, for the 

 feathery snow has done more to limit man's dominion of the 

 earth than any other of the unfriendly agencies of Nature, even 

 if we count the fiery ravage of the volcano and the ruinous work 

 of the earthquake. "While the rains are friends to man, and effi- 

 cient agents in the progress of civilization, the snows are his ene- 

 mies, and the most persistently hostile of his foes. 



It need scarcely be said that the invigorating beams of the sun 

 visit the earth in very differing measure, varying from tropical 

 profusion to frigid sparseness. This diversity of heat distribu- 

 tion is partly overcome by the agency of the winds and waters, 

 particularly the latter, since the great ocean currents carry vast 

 supplies of heat from the torrid zone toward the poles, and drive 

 far backward the boundaries of the realm of frost. The agency 

 of the air in this heat convection is of less importance. The anti- 

 trade winds move through the upper atmosphere, and lose their 

 heat before descending to the earth ; but surface winds from the 

 tropics convey a considerable share of the torrid heats to the 

 colder zones. 



Snow is the great opponent to the full effect of this distributed 

 heat. It constitutes an agent of Nature by which the chill of the 

 upper atmosphere is conveyed to the earth's surface, and stored 

 there in a more or less persistent form, which requires much of 

 the solar heat and the warmth of tropic winds and waters to over- 

 come. If it be asked how snow can produce such an effect, we 

 must advert to the heat relations of water. A large supply of 

 insensible heat latent heat, as it is called exists in liquid and 

 gaseous matter. In the freezing process this heat becomes sensi- 



