164 ANNUAL EEPOET SMITHSONIAN INSTITUTION, 1915. 



one at the lower, so arranged that 6 square feet of sunshine were con- 

 centrated onto 3 square feet of "hot box "; i.e., the concentration was 

 2 to 1. Its position Avas adjusted about every three weeks. This time 

 the total quantity of solar radiation collected was many times as large 

 as the largest collected by any previous worker, for the total area 

 was 10,296 square feet. In the best run of one hour this plant pro- 

 duced 816 pounds of steam at atmospheric pressure. This is at the 

 rate of 9 pounds per 100 square feet of sunshine, and therefore equiva- 

 lent to an allowance of 245 square feet of sunshine per brake horse- 

 power. The maximum thermal efficiency of this absorber was 29.5 

 per cent (pi. 4). 



Toward the end of 1911 the Sun Power Co. (Eastern Hemisphere), 

 (Ltd.), requested their consulting engineers (Messrs A. S. E. Acker- 

 mann and C. T. Walrond) to select and invite some distinguished 

 physicist to join them in a consultative capacity. Hence Prof. C. V. 

 Boys, F. R. S., became associated with the w^ork, and he suggested 

 a vital change in the design of the absorber, viz, that the boilers should 

 be placed on edge in a channel-shaped reflector of parabolic cross 

 section, so that solar radiation was received on both their surfaces, 

 instead of one being worse than idle, as it w^as when the boilers were 

 placed side on to the sun. The design immediately received the 

 hearty approval of the consulting engineers and Shuman, and at the 

 time we all thought the arrangement was novel, but the author has 

 since found and recorded herein that Ericsson used a very similar 

 reflector and boiler. 



An absorber of this design was constructed and erected at Meadi on 

 the Nile, 7 miles south of Cairo, in 1912, but the boiler was constructed 

 of thin zinc and failed before the official tests could be made. This 

 boiler was replaced by a cast-iron one in 1913, and the author (accom- 

 panied by his old pupil, G. W. Hilditch, A. M. Inst. C. E., as his chief 

 assistant, now Lieut. Hilditch of the Divisional Engineers, Royal 

 Naval Division) spent two most interesting months with the plant in 

 July and August, 1913. He went out in time to tune up the Shuman 

 engine (a 100-horsepower one) taken out from Tacony, and make all 

 the necessary preparations for the trials, of which there were over 35. 



In addition to the alteration of the shape of the reflectors, another 

 very important change was made. Their axes were placed north and 

 south, and they were automatically heeled over from an eastern aspect 

 in the morning to a western one in the evening, so as to follow the 

 sun. Thus the same number of solar rays were caught all day long, 

 and the small decrease in steam production in the morning and even- 

 ing was almost entirely due to the greater thickness of atmosphere 

 through which the rays had to pass. The total area of sunshine col- 

 lected was 13,269 square feet (pis. 5 and 6). 



