UTILIZATION OF SOLAR ENERGY ACKERMANN, 157 



In concluding this brief account of Adams's work you will be 

 pleased to learn that he was awarded the gold medal of the Sassoon 

 Institute of Bombay for his essay on The Utilization of Solar Heat, 

 which he submitted in JNIarch, 1878. 



In Comptes Eendus, Volume 91, 1880, pages 38&-389, M. Abel Pifre 

 claims an efficiency of 80 per cent for his apparatus when he says he 

 obtained a rate of absorption of 1.21 calories per square-centimeter- 

 rainute. If such a rate were obtained we now know it would mean an 

 efficiency of 89.7 per cent, which is improbable. Pifre used a para- 

 bolic reflectoi- (instead of a truncated cone), and reduced the surface 

 of the boiler, thus increasing the concentration. The capacity of his 

 boiler was 11 gallons, and he collected 100 square feet of solar radia- 

 tion so the diameter of his reflector was about 11 feet 4 inches. He 

 used a rotary pump, and raised 99 liters of water 3 meters in 14 

 minutes, which is equivalent to 0.065 horsepower. He ran a printing 

 press with his sun-power plant, and claimed that if he had collected 

 216 square feet of radiation he could have produced 1 horsepower, 

 which is quite likely (pi. 2). 



Next in order we have Langley's work, which consisted of many ex- 

 periments to determine the value of the solar constant, the value of 

 which he gave as 3 calories per square-centimeter-minute. 



Langley experimented wdth de Saussure's " hot box," and was the 

 leader of the expedition to Mount Whitney, where some of his best 

 work was done. He gave a j^reliminary account of this trip in Nature 

 of August 3, 1882, pages 314-317, and a full record of it under the 

 title " Researches on solar heat " in the United States of America 

 War Department, Papers of the Signal Service, 15, 1884. He also 

 referred to it in the New Astronomy (1900). 



In Nature (p. 315) , he said : 



As we stiU .slowly ascended and the surface temperature of the soil fell to the 

 freezing point, the solar radiation became intenser, and many of the party pre- 

 sented an appearance as of severe burns from an actual fire, while near the sum- 

 mit the temperature in a copper vessel, over which were laid two sheets of plain 

 window glass, rose above the boiling point, and it was certain that we could boil 

 water by the direct solar rays in such a vessel among snow fields. 



In Volume 73 of the Proceedings, Inst. C. E., 1883, page 284, 

 is described a plant designed by J. Harding, M. Inst. C. E., for dis- 

 tilling water by solar radiation. 



This plant w^as erected at Salinas, Chile, 4,300 feet above sea level, 

 and had 51,200 square feet of glass arranged in sections 4 feet wide, 

 and in the form of a very flat A, forming the roof of a shallow water 

 trough. The sun evaporated the water, and the resulting vapor con- 

 densed on the glass, for the temperature in the box was far higher 

 than that of the atmosphere, and hence of the glass. The pure water 

 trickled down the sloping glass and dripped from its lower edge into 



