3 o THE POPULAR SCIENCE MONTHLY. 



down in a ring around the place of the proposed excavation. A 

 brine, cooled to within a few degrees of (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 pro- 

 cess 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." * 



-- 



FORTIFYING AGAINST DISEASE.f 

 Bt sheridan delepine, m.b. 



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 



* 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. 



f 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. 



