160 



ANNUAL EEPORT SMITHSONIAN INSTITUTION, 1915. 



Preston's Treatise on Heat, it is stated that " mirror glass 2.6 milli- 

 meters thick transmitted 39 per cent of the radiation that fell on it 

 from a Locatelli lamp, while rock salt transmitted 92 per cent." The 

 diathermancy of each substance varies with the nature of the source 

 of heat, so the result just given is not comparable with that given by 

 Eneas. 



Abbot found the following percentages of heat were transmitted 

 through sheets of glass, each from 1.5 to 2 millimeters thick. In 

 one set of experiments the glass was normal to the rays and the other 

 at 45°. 



The sun-power plant known as the Pasadena ^ one was described 

 and illustrated in the August, 1901, issue of Cassier's Magazine by 

 Prof. E. H. Thurston, LL. D., D. E., and on page 103 of the Railway 

 and Engineering Review of February 23, 1901. It is stated to have 

 been designed by, and erected at the expense of, " a party of Boston 

 inventors whose names have not been made public." It consisted of 

 a truncated cone reflector, 33 feet 6 inches in diameter at the larger 

 end and 15 feet diameter at the smaller, with a boiler 13 feet 6 inches 

 long, having a capacity of 100 gallons (TJ. S. A.) plus 8 cubic feet 

 of steam space (pi. 3). 



The article in the Railway and Engineering Review states: 

 "According to newspaper accounts, the all-day average work per- 

 formed by the engine is 1,400 gallons (U. S. A.) of water lifted 

 12 feet per minute, which is at the rate of 4 horsepower." It is more 

 nearly 4^ horsepower; thus, this plant required 150 square feet of 

 radiation per horsepower, and the concentration appears to have 

 been 13.4. 



The Pasadena plant is said to have cost £1,000, and Willsie, writing 

 of it in 1909, says it was "the largest and strongest of the mirror 

 type of solar motor ever built." 



H. E. Willsie and John Boyle, jr., started their work in America 

 in 1902. The method they adopted was to let the solar radiation pass 

 through glass and heat water, which in turn was used to vaporize 



1 There appear to have been several plants erected at Pasadena by different experi- 

 menters. Probably Eneas designed the plant above described- 



