UTILIZATION OF SOLAR ENERGY ACKERMANN. 



147 



21, 1837, et seq.), all of which, aftei* a moderate length of expo.sure, 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 hy means of a tinned iron vessel of inches diameter, and 2.4 

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

 vertical rays of the sun 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 between De- 

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

 per minute, the c^uantity of water being 1,638 grains. Allowing for 

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

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

 ticulars we are able to calculate that Herschers value of the solar 

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

 centimeter-minute, while if we assume the coefficient of atmospheric 

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

 1.98, agreeing well with 1.93, the value now 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 velocity of light (186,000 miles per second), 

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

 without at all reducing the temperature of the sun. 



For comparison with Herschel's sand temperatures recorded above, 

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

 Meadi, Eg}'pt : 



