UTILIZATION OF SOLAR ENERGY ACKERMANN. 



159 



The water circulated up between the inner and outer steel tubes and 

 down the inner tube. The boiler was placed at the axis of the cone. 

 Its length was 13 feet 6 inches, its water capacitj^ 834 pounds (13.4 

 cubic feet), and steam space 8 cubic feet. Hence the diameter of 

 the outer tube appears to have been 1 foot 2 inches and the concen- 

 tration of radiation 13.4; i. e., 13.4 square feet of sunshine were con- 

 centrated on each square foot of the external surface of the boiler. 



C. G. Abbot (The Sun, p. 369) states that Eneas gave him the 

 following particulars : 



February U, i90J.— Pasadena, Cal., 11.30 a. m.-0.30 p. m. ; 642 square feet 

 sunshine. Temperature of air, 61° F. Steam pressure, 145-151 pounds per 

 square inch. Steam condensed, 123 pounds. 



October 3, 1903. — Mesa, Ariz., " about midday " ; 700 square feet sunshine. 

 Temperature of air 74° F. Average steam pressure, 141 pounds per square incli. 

 Steam condensed, 133 pounds. 



October 9, 190^. — Willcox, Ariz., 11 a. m.-12 a. m. ; 700 square feet sunsliine. 

 Steam pressure, 148-156 pounds per square inch. Steam condensed, 144.5 

 pounds. 



The temperature of the feed water is not given, but, assuming it 

 to be the same as the temperature of the air, we can deduce the rate 

 of absorption per square foot of radiation and the thermal elRciency 

 of the absorber. This being done, we obtain the following table : 



> For a maximum transmission of radiation through the atmosphere of 70 per cent. 



Eneas refers to his " nine different types of large reflectors," and 

 found that he obtained better results when he concentrated the re- 

 flected rays " on two parts of the boiler instead of its entire length, 

 as in the Pasadena machine." The unexposed portions of the boiler 

 then appear to have been lagged. 



Eneas said, " I find 3.71 B. t. u. per square foot per minute as the 

 greatest amount of heat obtainable during tlie trial runs." This 

 gives a maximum efficiency of 74.5 per cent, which agrees with the 

 result given for his Pasadena plant in the foregoing table. 



Eneas also stated that " the interposition of a single thin glass 

 plate in a beam of sunlight diminishes the intensity about 15 per cent. 

 This decrease is owing principally to reflection." On page 466 of 



