of the Solar Spectrum. 239 



fore, to the deflection shown by the thermo-battery when sub- 

 jected to the coloured rays, that deflection must also be taken 

 into account which occurs before and after the experiment when 

 the thermo-battery is protected as much as possible from all 

 radiation. A series of experiments of this kind will render this 

 clear : — 



Deflecting 

 forces. 



273 

 140 



52 



91 



13 



The " deflecting forces" given in the last column are easily 

 calculated from the previous column of numbers. When the 

 solar rays before falling upon the thermo-battery had to pass 

 through pure water, the deflection was 56°. This deflection, 

 according to the Table (page 236), corresponds with the strength 

 of current 130. To this strength of current 10 has still to be 

 added. 



After these remarks, which sufficiently explain the process of 

 the experiments, it will be sufficient so to arrange the three best 

 series of experiments that the thermal efiect of the rays which 

 have passed through colourless water is denoted by 100. 



The fact that the sum of the quantities of heat which pass 

 through the yellow, the green, and the blue solution (». e. 

 70 + 9 + 9 = 88) is not equal to the amount of heat which passes 

 through colourless water, 100, evidently depends upon the ab- 

 sorption by each solution of some of the rays of its own colour : 

 just as wc already know that the green solution does not allow 

 the passage of all the green rays of the spectrum. If w'e divide 

 the diff"erence, 100 — 88 = 12, in such a manner that 2 are given 

 to red, 2 to orange and yellow, 4 to green and 4 to blue, indigo, 

 and violet, then numbers expressing the warming power of the 



