UTILIZATION OF SOLAR ENERGY ACKERMANN. 163 



Frank Shumaii, of America, started on the problem in 1906, and 

 in 1907 he had a plant running which developed about 3^ horsepower ; 

 1,200 square feet of sunshine fell onto a fixed, horizontal water box 

 with a glass top. In the water there were rows of parallel horizontal 

 black pipes containing ether, and exposing 900 square feet of surface 

 to the solar radiation. The water also became heated and conveyed 

 heat to the under sides of the pipes. The ether boiled, and its 

 " steam " drove a small vertical, simple, single-cylinder engine. The 

 exhaust ether vapor passed into an air surface condenser, and the 

 liquid ether from this was pumped back into the tubes of the " boiler " 

 already described. 



This plant, Shuman saj^s, ran well even when snow was lying on 

 the ground. This at first seems very remarkable, but though in the 

 winter the number of solar rays falling on a given horizontal area is 

 smaller than in summer, the permeability of the atmosphere is about 

 20 per cent greater in winter than in summer, which counteracts the 

 other effect; but of course the loss of heat by conduction from the 

 boiler is greater in winter than in summer. 



In 1910 Shuman constructed an experimental unit of an absorber 

 measuring 6 by 9 feet. This unit combined the lamellar boiler of 

 Tellier and the " hot box " of de Saussure, for it consisted of a shallow 

 black box with double glass top, with 1 inch of air space between 

 the two layers of glass, another air space of an inch between the lower 

 glass and the boiler, which was 6 feet long (up the slant), 2 feet 6 

 inches wide, and l inch thick over all. The box was so sloped that 

 at noon the rays of the sun were perpendicular to the glass. The box 

 was not moved to follow the sun, but it was adjusted about every three 

 weeks, so that the condition just named was complied with. The 

 remarkable thing about the absorber was that there was no concentra- 

 tion of any kind of the sunshine by mirrors, lenses, or other means, 

 and yet the author on one occasion recorded a temperature of 250° F. 

 in the box. The best run of an hour's duration produced steam at 

 atmospheric pressure at the rate of 7h pounds per 100 square feet of 

 sunshine falling on the box. The author's tests of a Shuman 100 

 horsepower low-pressure engine at Erith showed the steam consump- 

 tion to be 22 pounds at atmospheric pressure per brake-horsepower- 

 hour. Hence, with an absorber of the type just described, it would 

 be necessary to collect solar radiation to the extent of 300 square feet 

 per brake horsepower, which is a much larger area than any named 

 by other workers. The maximum thermal efficiency of this absorber 

 was 21.1 per cent. 



In 1911, with the aid of some English capitalists, Shuman con- 

 structed his third absorber at Tacony (a suburb of Philadelphia), 

 which was almost identical with the one just described, except that it 

 had two plane mirrors, one at the upper edge of the " hot box " and 



