514 STATE BOARD OF AGRICULTURE. 



On account of these obstacles, also because of the fact that the ac- 

 curacy of the thermopile is considerably reduced by the many acci- 

 dental electrical currents, the thermopile, as a radiometer, was finally 

 abandoned in favor of a Beckmann thermometer. This thermometer gave 

 very satisfactory results. 



The complete apparatus employed for the study is shown by diagram 

 3. With the exception of part 'SI, it is the same as in Fig. I. The 

 part or vessel M is a box in which was placed the sand whose radiation 

 was to be studied. It is made all of copper and it is 6 inches in each 

 dimension. Inside of all four sides were placed asbestos strips i/s-inch 

 thick and about 10 inches high, or 4 inches higher than the sides, and 

 extending to the bottom — they were intended to prevent any side radia- 

 tion from the copper vessel or other sources to the thermometer. The 

 box was filled with the sand to a certain height so that the upper surface 

 of the sand would be even with the upper surface of the water in the 

 constant temperature bath, and was left in the latter about 24 hours 

 in order to acquire the constant temperature. The thermometer was 

 placed about one inch from the surface of the sand and its bulb was 

 protected from any side radiations by the cone or hood. 



Near the radiation receiving lieckmann thermometer was placed an- 

 other Beckmann thermometer to indicate the room temperature. Their 

 readings were taken simultaneously and when the reading of the first 

 thermometer is divided by that of the second, a ratio is obtained which 

 is designated as the radiating power of any particular color or soil. 

 Throughout this investigation, then, the relative radiating power of 

 ditTerent materials is reduced to this ratio. 



This method of measuring the radiating power of substances gave 

 most satisfactory results. If the room temperature was exactly the 

 same the readings of duplicate experiments could be checked to less 

 then 1%. In the measurement or study of the radiating power of 

 any color or soil, therefore, the readings of the two thermometers were 

 taken when the room temperature was about the same as in the previous 

 or standard experiment and the variation did not exceed 0.2° C. To 

 eliminate also any errors that may arise on account of the different re- 

 flective powers of the various materials, the readings were taken in 

 every case in dark. 



EFFECT OF COLOR ON RADIATION. 



There were six different colored sands in which the radiation was 

 measured by the foregoing method. These were white, black, blue, 

 green, red and yellow. The white was the uncolored sand. The results 

 obtained are given herewith : 



TABLE 13.— THE RADIATION OF DIFFERENT COLORED SANDS. 



