602 TRANSACTIONS OP THE AMERICAN INSTITUTE. 



conclusions are : 1st. That the height of the atmosphere, presupposing an 

 equal power of absorption in the different superimposed strata of air, is 

 only equivalent to the 173d part of the earth's radius. 2d. The amount of 

 heating power of the sun's rays, on entering this atmosphere, is determined 

 by the fact that a beam of rays, a square inch in cross section, would 

 during one minute elevate the temperature of a cubic inch of water 0.133 

 of 1"^ Centigrade. 3d. The loss of heat in its passage through the atmos- 

 phere, taken on different days and seasons, and when the air is apparently 

 clear, is variable. 



Pouillet found the heat of the sun's rays one-eighth part smaller, but he 

 gave the atmosphere a height of one-eightieth of the earth's radius. Tlie height 

 of the atmosphere, according to Hagan, is a little more than twenty-three 

 miles ; according to Pouillet, 50 miles. The following table shows its 

 density at increasing heights, and the height of the mercurial column, cor- 

 responding : 



Height in miles. Volume. Barom. in inches. 



1 30 



2.705 2 15 



5.41 4 7.5 



8.115 8 3.75 



10.82 16 1.875 



13.525 32 .9375 



1G.23 64 .46875 



Great Railway Bridge. 



The new bridge now being built on the railway route leading from New 

 York to Washington, across the Susquehanna river at Havre de Grace, 

 will be 3,300 feet long, and supported by thirteen stone piers, -each 240 

 feet apart ; seven of these will have pile foundations and six rock. They 

 •will be constructed so as to resist the greatest pressure of ice which it is 

 possible to bring against them. The greatest depth of water in which 

 these piers are laid is forty-two feet. The bridge will have " a draw" on 

 the pivot plan, with two openings of seventy feet each in width. The rail- 

 way track will be twenty-five feet from the water ; above that will be a 

 common carriago-way. The entire height of the bridge will be fifty feet- 

 its estimated cost is $700,000. It was intended to build the superstructure 

 of iron, but the high price of that material may cause the substitution of 

 wood. 



Surface Steam Condensers. 



The selected subject was then taken up. 



Mr. S. H, Mayuard opened the discussion by alluding to the difference 

 between surface and jet condensation, which had been fully explained at 

 the last meeting. The inquiry was tten made, that as the cost of con. 

 structing the surface condenser was greater than that of jet condenser, 

 what was the money value to induce owners of steamships to adopt it ? 

 And in answer he presented the following comparative statement of value 

 of jet and surface condensation, as shown by the log of the Sonora, Pacific 

 Mail Steamship Company's steamer, during five consecutive trips with each 

 kind of condenser. 



