THE SOLAll FORCES. 1GO 



facility. .In bending the ray of white light out of its 

 path, by means of a triangular piece of glass, we divide 

 it in a remarkable manner. We learn that heat is less 

 refracted by the glass than the other powers ; we find 

 the maximum point of the calorific rays but slightly 

 thrown out of the right line, which the solar pencil would 

 have taken, had it not been interrupted by the prism; 

 and the thermic action is found to diminish with much 

 regularity on either side of this line. We discover that 

 the luminous power is subject to greater refraction, and 

 that its maximum lies, considerably above that of heat ; 

 and that, in like manner, on each side the light 

 diminishes, producing orange, red, and crimson colours 

 below the maximum point, and green, blue, and violet 

 above it. Again, we find that the radiations which 

 produce chemical change are more refrangible than 

 either of the others, and the maximum of this power is 

 found at the point where light rapidly diminishes, and 

 where scarcely any heat can be detected : it extends in 

 full activity, above its maximum, to a considerable dis- 

 tance, where no trace of light under ordinary conditions 

 exists, and below that point, until light, appearing to 

 act as an interfering agent, quenches its peculiar pro- 

 perties. These are strong evidences that light and 

 actinism ' as this principle has been named are not 

 identical : and we may separate them most easily and 

 effectually from each other. Certain glasses, stained 

 dark blue, with oxide of cobalt, admit scarcely any 

 light; but they offer .no interruption to the passage of 

 actinism or the chemical rays ; on the contrary, a pure 

 yellow glass, or a yellow fluid, which does not sensibly 

 reduce the intensity of any one colour of the chromatic 

 band of luminous rays, completely cuts off this chemical 

 principle, whatever it may be. In addition to these, 

 there are other results which we shall have to describe, 

 which prove that, although associated in the solar beam, 

 light and actinism are in constant antagonism. 



