EXPERIMENT STATION BULLETINS. 



515 



The first column of figures from the left represent the relative radia- 

 tion ratio. The last colunm contains the same data reduced to the 

 percentage basis with the white sand as 100% or unit. A glance at 

 these figures reveals at once the fact that the radiating power of the 

 different colored sands is the same, the greatest range being between 

 the white and green sands which is only 1.88% and which is quite Avithin 

 the experimental error. 



From these data wo are justified in concluding that color has no efifect 

 on radiation, at least at this low temperature. It does have on absorp- 

 tion, however, as will be shown below. 



EFFECT OF COLOR OX ABSORPTION OF HEAT. 



This study was conducted by filling wooden boxes 12 inches square, 

 2 inches high with bottom and no top, with the various colored sands em- 

 ployed in the preceding investigation, placing them outdoors during 

 hot and clear days and recording the temperature at various intervals 

 for 24 or more hours, with mercury thermometers graduated to 0.1° C. 

 There were several experiments conducted but for the sake of brevity 

 onlv two are given here. The first was conducted on Julv 27 when 

 the sky was perfectly clear from early morning till about 6 in the after- 

 noon. From this hour on the sky was clouded and about five o'clock the 

 next morning it began to rain. The temperature records were taken 

 every hour during all this time. The second experiment was performed 

 on August 5. This day was also hot and the sky perfectly clear from 

 clouds from morning till evening and even on the succeeding day. The 

 temperature was recorded every hour till the maximum was attained 

 and then at various intervals till late at night, again at 4:30 the next 

 morning before the sun appeared. In the table below, however, only 

 the maximum and minimum readings of both experiments are given. 

 The minimum readings were taken in order to obtain further light 

 on the effect of color on radiation. 



The figures obtained at both times show that the various colors have 

 a most significant different absorptive power for the rays of the sun. 

 The black absorbed the greatest amount and hence attained the high- 

 est temperature, followed in order by blue, red, green, yellow and white, 



