154 ANNUAL EEPOET SMITHSONIAN INSTITUTION, 1915. 



is effected by means of a horizontal axle, concealed by the trough, the entire 

 mass being so accurately balanced that a pull of 5 pounds applied at the extrem- 

 ity enables a person to change the inclination or cause the whole to revolve. 

 A single revolution of the motive engine develops more power than needed to 

 turn the trough, and regulates its inclination so as to face the sun during a day's 

 operation. 



The motor shown by the illustration is a steam engine, the working cylinder 

 being 6 inches in diameter, v/ith 8-inch stroke. The piston rod, passing 

 through the bottom of the cylinder, operates a force pump of 5 inches diameter. 

 By means of an ordinary crosshead secured to the piston rod below the steam 

 cylinder, and by ordinary connecting rods motion is imparted to a crank shaft 

 and fly wheel, applied at the top of the engine frame, the object of this arrange- 

 ment being that of showing the capability of the engine to work either pumps or 

 mills. It should be noticed that the flexible steam pipe employed to convey the 

 steam to the engine, as well as to the steam chamber attached to the upper 

 end of the heater, have been excluded in the illustration. The average speed of 

 the engine during the trials last summer was 120 turns per minute, the absolute 

 pressure on the working piston being 35 pounds per square inch. The steam 

 was worked expansively in the ratio of 1 to 3, v.'ith a nearly perfect vacuum 

 kept up in the condenser inclosed in the pedestal which supports the engine 

 frame. 



In view of the foregoing, experts need not be told that the sun motor can be 

 carried out on a sufficient scale to benefit very materially the sun-burnt regions 

 of our planet. 



From the particulars given it is easily calculated that the " con- 

 centration " of this absorber was 9. 



The Eev. C. H. Pope has produced a useful little book entitled 

 " Solar Heat," the second edition of which was published in 1906. 

 In it he tells us he started his experiments (which do not appear to 

 have included the conversion of solar radiation into mechanical 

 energy) in 1875. He used a modification of Mouchot's truncated 

 cone reflector formed of many plane mirrors, the plan adopted about 

 the same time by Adams. Pope has fallen into the same error re the 

 connection between temperature and concentration of radiation as 

 did Adams, for he says (p. 17) : 



That the degree and amount of heat at the focus will be proportionate to the 

 area of the opening of the lens or mirror, and that thus the only limit to the 

 temperature which may be reached is the size to which such lenses and mirrors 

 may be constructed and revolved. 



And (p. 93) : 



These rays may, therefore, be gathered together and made to unite, as if they 

 became one denser, stronger, hotter ray, so that the temperature of the con- 

 densed rays will be raised in proportion to the number of rays blended, and 

 we can thus cause the heat to increase to any degree our apparatus can be 

 enlarged. 



W. Adams, deputy registrar, High Court, Bombay, seems to be the 

 sole Englishman who has worked on the practical side of the prob- 

 lem of the utilization of solar energy. His work was done in India, 

 and is recorded in his interesting book. Solar Heat (Bombay, 



