UTILIZATION OF SOLAR ENEEGY ACKEEMANN. 



147 



21, 1837, et seq.), all of which, after a moderate length of exposure, were found 

 perfectly cooked, the eggs being rendered hard and powdery to the center ; and 

 on one occasion a very respectable stew of meat and vegetables was prepared, 

 and eaten with no small relish by the entertained bystanders. 



Sir John then described his method of determining the solar con- 

 stant by means of a tinned iron vessel 3^ inches diameter, and 2.4 

 inches high filled with inked water, upon which he allowed the nearly 

 vertical rays of the sim to play through a 3.024-inch-diameter hole 

 for 10 minutes and noted the rise in temperature, of course allowing 

 for cooling losses. The mean of six experiments, made betAveen De- 

 cember 23, 1836, and January 9, 1837, inclusive, gave a rise of 0.38° F. 

 per minute, the quantity of water being 4,638 grains. Allowing for 

 the obliquity of the sun's rays, the mean area of the normal cross-sec- 

 tion of the beam of sunlight Avas 7.01 square inches. From these par- 

 ticulars AA'e are able to calculate that Herschel's a alue of the solar 

 radiation reaching the earth's surface was 1.38 calories per square- 

 centimeter-minute, Avhile if Ave assume the coefficient of atmospheric 

 transmission to have been 0.70, his value of the solar constant Avas 

 1.98, agreeing wxU Avith 1.93, the A^alue noAV accepted as correct. 



From these experiments he deduced that a cylindrical rod of ice, 

 45.3 miles in diameter, and of indefinite length, continually darted 

 into the sun with the Aelocity of light (186,000 miles per second), 

 would barely suffice to employ the whole radiant heat for its fusion, 

 Avithout at all reducing the temperature of the sun. 



For comparison with Herschel's sand temperatures recorded above, 

 the author gives the following similar readings, which he obtained at 

 Meadi, Egypt : 



