Page:Popular Science Monthly Volume 25.djvu/817

Rh walls or ceiling of the chamber to be cooled. The discharge-pipe of the circulating pump communicates with a condenser, which consists of a tubular vessel immersed in a tank containing cooling water taken from any convenient source and kept in constant circulation. The volatilized liquid is expelled from the pump into this condenser, where the process of condensation or liquefaction of the gas is completed. The restored liquid is then returned to the refrigerator by suitable connections, to be again volatilized, and so on continuously, the waste of the agent being but trifling.

The time consumed in the process of freezing the water-cans ranges from twenty-four to thirty-six hours. The more perfect the insulation of the tanks in which the water-cans are immersed, the more quickly is the latent heat extracted from the water; and this, after all, is the problem involved in artificial freezing. To speak of the manufacture of cold, though popularly comprehensible and convenient, is to misapply terms. In one sense heat seems to be but an incident of the cosmic order, an exception to a state of things pervading interstellar space, and toward which the warm earth, and her sister planets, and all the burning orbs of heaven, are gradually tending. In producing cold we therefore seem but to assist Nature to restablish, in an infinitesimal degree, the state of comparative molecular inactivity that distinguishes cold from heat, and which characterizes the vacuum.

The need of an efficient system of artificial refrigeration is constantly increasing. Not alone in warm countries is ice rapidly becoming a universal necessity, but, in myriad industries in temperate climes, the economy experienced by using air-cooling contrivances in the place of Nature's unwieldy, slippery, and not always obtainable product, has long since been satisfactorily demonstrated by the widespread use of various systems of machines.

In the years to come, there may arise some engineering genius bold enough to conceive and skillful enough to execute a plan for tapping the limitless reservoir of cold that pervades interplanetary space, and bringing a supply, regulable at will, to a sweltering world. This would be a highly satisfactory solution of the problem of such interest to nine tenths of humanity for a large portion of the year, how to keep cool. Pending, however, the realization of such a scheme, of which it must be confessed there is no immediate prospect, it is difficult to discern any way to an improvement, in this branch of physics, on the latest product of French inventive genius.