2l8 



NATURE 



iJcm. 3, 1884 



of flat window glass silvered on the under side, are 

 fastened. It will be readily understood that the method 

 thus adopted for concentrating the radiant heat does not 

 call for a structure of great accuracy, provided the wooden 

 staves are secured to the iron ribs in such a position that 

 the silvered plates attached to the same reflect the sokr 

 rays towards the heater. F^ig. 2 represents a transverse 

 section of the latter, part of the bottom of the trough, and 

 sections of the reflecting plates ; the direct and reflected 

 solar rays being indicated by vertical and diagonal lines. 

 Referring to the illustration, it will be seen that the 

 trough, II feet long, and 16 feet broad, including a 

 parallel opening in the bottom, 12 inches wide, is sus- 

 tained by a light truss attached to each end ; the heater 

 being supported by vertical plates secured to the truss. 

 The heater is (i\ inches in diameter, 1 1 feet long, exposing 

 130 X 9'S = 1274 superficial inches to the action of the 

 reflected solar rays. The reflecting plates, each 3 inches 

 wide and 26 inches long, intercept a sunbeam of 130 X 



180 = 23,400 square niches section. The trough is sup- 

 ported by a central pivot, round which it revolves. The 

 change of inclination is effected by means of a horizontal 

 axle — concealed by the trough — the entire mass being 

 so accurately balanced that a pull of five pounds applied 

 at the extremity enables a person to change the inclina- 

 tion or cause the whole to revolve. A single revolution 

 of the motive engine develops more power than needed 

 to turn the trough, and regulate 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, with 

 8 inches stroke. The piston rod, parsing through the 

 bottom of the cylinder, operates a force-pump of 5 inches 

 diameter. By means of an ordinary cross-head secured 

 to the piston-rod below the steam cylinder, and by ordi- 

 n ay connecting rods, motion is imparted to a crank 

 sluilt and fly-wheel, applied at the top of the engine 



frame ; the object of this arrangement 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 the steam chamber attached to the upper end of the 

 heater, have been excluded in the ilkistration. 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 lbs. per square inch. The steam 

 was worked expansively in the ratio of i to 3, with 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. 



With reference to solar temperature, the power deve- 

 loped by the sun motor establishes relations between 

 diffusion and energy of solar radiation which show that 

 Newton's estimate of solar temperature must be accepted. 

 The following demonstration, ba:ed on the foregoing 

 particulars, will be readily comprehended. 



The area of a sphere whose radius is equal to 

 the earth's mean distance from the sun being to 

 the area of the latter as 2i4'5- : i, while the reflector of the 

 solar motor intercepts a sunbeam of 23,400 square inches 

 section, it follows that the reflector will receive the heit 



developed by "-""^ = o'5o8 square inch of the solar 



2r4-5- 

 surface. Hence, as the heater of the motor contains 

 1274 square inches, we establish the fact that the re- 

 flected solar rays acting on the same are diffused in the 

 ratio of 1274 :o'5oS = 2507 : i. Practice has now shown 

 that, notwithstanding this extreme diffusion, the radiant 

 energy transmitted to the reflector by the sun is capable 

 of imparting a temperature to the heater of 520' Fahr. 

 above that of the atmosphere. The practical demonstra- 

 tion thus furnished by the sun motor enables us to deter- 

 mine with sufficient exactness the minimum temperature 

 of the solar surface. It also enables us to prove that the 

 calculations made by certain French scientists indicating 

 that solar temperature does not exceed the temperatures 

 produced in the laboratory are wholly erroneous. Had 

 Pouillet known that solar radiation, after suffering a two- 

 tJwnsand-five-hund7-cd-and seiicn-fold diftusion, retains a 

 radiant energy of 520° Fahr., he would not have asserted 

 that the temperature of the solar surface is 1760° C. 

 Accepting Newton's law that " the temperature is as the 

 density of the rays,'' the temperature imparted to the 

 heater of the sun motor proves that the temperature of 

 the solar surface cannot be less than 520-" X 2507 = 

 1,303,640" Fahr. Let us bear in mind that, while attempts 

 have been made to establish a much lower temperature 

 than Newton's estimate, no demonstration whatever has 

 yet been produced tending lo pror'f that the said law is 

 unsound. On the contrary, the most careful investiga- 

 tions show that the temperature produced by radiant heat 

 emanating from incandescent spherical bodies diminishes 

 inversely as the diffusion of the heat rays. Again, the 

 writer has proved by his vacuum-actinometer, inclosed in 

 a vessel maintained at a constant temperature during the 

 observations, that for equal zenith distance the intensity of 

 solar radiation at midsummer is 5°88 Fahr. less than during 

 the winter solstice. This diminution of the sun's radiant 

 heat in aphelion, it will be found, corresponds within 

 o 40 of the temperature which Newton's law demands. 

 It is proposed to discuss this branch of the subject more 

 fully on a future occasion. 



The operation of the sun motor, it will be well to acid, 

 furnishes another proof in support of Newton's assump- 

 tion that the energy increases as the driisi/y of the ra\s. 

 The foregoing explanation concerning the reflection of 

 the rays (see Fig. 2), shows that no augmentation of 

 temperature takes place during their transmission from 



