144 



ANNUAL REPORT SMITHSONIAN INSTITUTION, 1915. 



steam increased about 30 per cent, thus showing the great importance 

 of humidity in connection with this subject. 



The great possibilities of this field of work, and the obvious fact 

 that there is a limit to our supplies of coal and oil, have naturally 

 attracted many workers, of whom the following is a chronological list. 

 Some of them, however, have not been engaged in the practical 

 utilization of solar energy, but in determining the solar constant and 

 atmospheric absorption which tell us the theoretical qiumtity of heat 

 available for power purposes. 



Name. 



Solomon de Caux ( France) 



H. B. de Saussure (Sweden) 



Sir John Herschel (England) 



C. S. M. Pouillet (France) 



C. L. Althans (Germany) 



Carl Giintner (Austria) 



August Mouchot (France) 



John Ericsson (United States of America) . 



C. H. Pope (United States of America) 



William Adams (England) 



Abel Pifre (France) 



S. P. Langley (United States of Amcricix).. 



J. Harding (England) 



Chas. Loms Abel Tellier (Franco) 



A. G. Eneas (United States of America). . . 



H. E. Willsie 



C. G. Abbot (United States of America)... 

 Frank Shuman (United States of America) 



Ch. F^ry (France) 



G. Millochau ( France) 



Date of 

 birth. 



1576 

 1740 

 1792 

 1791 



(?) 



(?) 



(?) 

 1803 



(?) 



(?) 



(?) 

 1S31 



(?) 



(?) 



(?) 



(?) 

 1872 

 1802 

 1865 

 1S71 (?) 



Date of 

 death. 



1626 

 1799 

 1871 

 1868 

 (?) 

 (?) 

 (?) 

 1889 

 (?) 

 (?) 

 (?) 

 1906 

 (?) 

 1913 



Date of 



first solar 



work. 



1615 

 1766 

 1836 

 1838 

 1853 

 1854 

 1860 

 1864 

 1875 

 1876 

 1878 

 1881 

 1883 

 ,1884 

 1900 

 1902 

 1905 

 1906 

 1906 

 1906 



Now, although the theoretical power value of the heat reaching the 

 surface of the earth is no less than 5,000 horsepower per acre, it must 

 not be thought that anything like this amount can be converted into 

 mechanical power any more than can all the heat of coal be converted 

 into its theoretical equivalent of mechanical power. For example, 

 the heat value of good coal is about 11,500 B. t. u. per pound, equal 

 to 12,760 horsepower hours per ton, but in fact the best result, even 

 imder test conditions, ever obtained from a ton of coal by means of a 

 boiler and steam engine is only about 1,470 brake horsepower hours, 

 or 11.5 per cent of the heat value, while in the case of a gas engine the 

 corresponding figure is 25.5 per cent, and of a Diesel oil engine 31 per 

 cent. The chief loss is in converting the steam into mechanical energy, 

 and most of the loss is inevitable for thermodynamic reasons. With 

 this fact in mind, you will not be so surprised to learn that the best 

 overall thermal efficiency obtained from the Shuman-Boys plant in 

 Egypt was only 4.32 per cent, the chief reasons for this being so much 

 less than 11.5 per cent being that the steam pressure was so low, and 



