200 



THE SCIENTIFIC -PAPERS OF 



of about 200 superficial feet of heat-absorbing surface 6 5 -20 = 

 45 cooler than the surrounding atmosphere on an ordinary 

 summer's day. The machinery especially being ill-protected, and 

 of a dark colour, I estimate the loss of effect from this source at 

 about 3'6 H.P., assuming that the covering prevents two-thirds of 

 the radiation which would take place if the surface were unpro- 

 tected. Assuming that the solution in the cylinder has been 

 reduced to 20 Fahrenheit, the total losses are as follows : 



By throttled passages, &c. 

 ,, agitation and friction 

 ,, condensation of vapour 

 ,, cold air leaving cistern . 

 ., absorption of heat from the atmo- 

 sphere 



see paragraph 1 



2 say 

 3 

 4 



H. P. 



10-08 

 3-00 



Total loss . 



Total power to be obtained 



3-60 



25-83 

 25-2 



It follows that when the temperature of the cistern is reduced 

 to 20, the losses of cold produced equal or actually exceed the 

 power of the apparatus of producing the same, which result is 

 corroborated sufficiently well by the experience obtained, although 

 it has been the result of independent calculation as regards para- 

 graphs 1, 3 and 4, but only assumed as regards paragraphs 2 

 and 5, which, however, are the less important. 



" The next question is whether, and to what extent, these 

 different sources of loss can be obviated ; and I will at once 

 proceed to describe the fresh arrangements I propose for your 

 adoption, and which are illustrated by the sketch shown 

 on Plate 36. 



" The proposed expanding and freezing apparatus consist of a 

 cylinder of cast iron of 17 inches diameter, instead of 19 inches, 

 and 4 feet 6 inches stroke. The pipes and valves connected with 

 this cylinder to have a sectional area of not less than 15 square 

 inches (instead of 7 square inches), and no stop-valve to be 

 introduced. The admission valves to cut off at one-fourth part 

 of the stroke. The expanding cylinder is immersed in the cistern 

 containing the freezing solution, and the expanded air issues from 



