Page:Popular Science Monthly Volume 39.djvu/40

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down in a ring around the place of the proposed excavation. A brine, cooled to within a few degrees of 0° (Fahr.), is sent down through an inner pipe and returns through the space between the two pipes. By this means a cylinder of the wet earth is frozen, within which the digging is done and the lining of the shaft put in place. The core of the cylinder which is to be removed will be partly or wholly frozen, according to the degree of refrigeration employed. Frozen quicksand looks like a fine-grained sandstone, and is about as hard to cut through.

Those who are acquainted with the history of invention, will not be surprised to learn that the Asiatics were centuries ahead of us in the making of ice, as in the use of gunpowder, the compass, etc. Ice has long been made in India by the following method: Pits two feet deep and twenty or thirty feet square are dug in a large, open field, and about half filled with straw. After sunset shallow dishes of porous clay are placed on the straw and water is poured into them. The rapid evaporation of part of the water, assisted by the radiation of heat from the straw, chills the water remaining, and, if the night is favorable, thin sheets of ice form in the pans by morning. The operation is most successful when the sky is clear and a gentle dry breeze is blowing. Although we of the Western world have clearly been anticipated in producing ice artificially, we may still claim the superior credit that our process has not remained stagnant for generations, but has achieved many of the possibilities that have been open to it, and become independent of such limitations as the state of the weather, and others that hamper the operations of the "gentle Hindoo." [1]



THE intense excitement and the unbounded hopes created by the announcement that a cure for consumption has at last been found have led me to lecture to-day on a subject which I generally relegate to the end of my course of pathology. For, after discussing the various phenomena which are brought about by disease, and attempting to connect these phenomena with their cause, apparent or real, it is natural to try to explain why these

  1. For the electrotypes of Figs. 2 and 5 in this article I am indebted to the courtesy of the De La Vergne Refrigerating Machine Company.
  2. On Development of Modern Ideas on Preventive, Protective, and Curative Treatment of Bacterial Diseases, and on Immunity or Refractoriness to Disease. A lecture delivered at St. George's Hospital on November 20, 1890, on the occasion of the publication of Koch's method for the cure of tuberculosis.