Heat in the Spectrum* 109 



by those experiments was that the heat in the invisible is eight 

 times that in the visible region. But had there been an error 

 in estimating the position of the extreme red by only two milli- 

 metres^ so much would have been taken from the invisible and 

 added to the visible that they would have been brought to equa- 

 lity, and then the slightest turn of the screw that carried the 

 pile toward the dark space would have given a preponderance to 

 the visible. It is obvious_, therefore, that there cannot be cer- 

 tainty in such measures unless the fixed lines are resorted to as 

 standard points. 



(2) A ray which has passed through a solution of sulphate 

 of copper and ammonia possesses no insignificant heating- 

 power. I took a stratum of a solution of that salt of such 

 strength that it only permitted waves to pass which are of less 

 length than 4860. Seen in the spectroscope, the colours trans- 

 mitted through it commenced with a thin green fringe, followed 

 by blue, indigo, violet. It therefore gave rays in which, accord- 

 ing to the accepted views, little or no heat should be detected. 

 Yet I found that such rays produced one ninth of the heat of 

 the entire solar beam. Does not this indisputably show that 

 the more refrangible rays have a higher calorific power than is 

 commonly imputed to them ? 



(3) Again, by the use of the apparatus presently to be de- 

 scribed, I found no difficulty in recognizing heat in the violet 

 region ; but in the mode of conducting the experiment hereto- 

 fore resorted to it could not be detected in rays more refrangible 

 than the blue. It was this result which gave so much weight to 

 the conclusion that in the more refrangible regions the calorific 

 power is replaced by chemical force, and strengthened the idea 

 commonly entertained that the solar radiations consist of three 

 distinct principles — heat, light, and actinism. In the memoir 

 above referred to as soon to be published, I shall present some 

 facts which apparently make this view indefensible. 



(4) If waves of light falling upon an absolutely black surface 

 and becoming extinct thereby are transmuted into heat, if the 

 warming of surfaces by incident light be nothing more than the 

 conversion of motion into heat — an illustration of the modern 

 doctrine of the correlation of forces, heat itself being only a 

 "mode of motion ^^ — it would seem extraordinary that this con- 

 version should cease in the green or blue or in any ray. On the 

 contrary, calorific effects ought to be traceable throughout the 

 entire length of the spectrum. These views on the transference 

 of motion from the sether to the particles of ponderable bodies, 

 and conversely, I endeavoured to explain in detail in a memoir on 

 Phosphorescence, inserted in the Philosophical Magazine, Peb. 

 1851, p. 98 &c. I had previously indicated them in the same 



