CALOHIFIC TRANSPARENT.. 67 



"We thus arrive at the fact that heat and light ma}' be 

 separated from each other ; aud if we examine the solar 

 beam by that analysis which the prism affords, we shall 

 find that there is no correspondence between intense 

 light and ardent heat. By careful observation, it has 

 been proved, when we have a temperature of 62 F. in the 

 yellow ray, which ray has the greatest illuminating power; 

 that below the red ray, out of the point of visible light, 

 the temperature is found to be 79, while at the other end 

 of the spectrum, in the blue ray, it is 56, and at the end 

 of the violet ray no thermic action can be detected.* 



From the circumstance, that as we, by artificial 

 means, raise the temperature of any body, and produce 

 intense heat, so after a certain point of thermic elevation 



* In the Philosophical Transactions, vol. xc., the following 

 papers, by Sir William Herschel, may be consulted : 



Investigation of the powers of the prismatic colours to heafand 

 illuminate objects ; with remarks that prove the different re- 

 franyibility of radiant heat. To which is added, an inquiry into 

 the method of viewing the sun advantageously, with telescopes of 

 large apertures and high magnifying powers, p. 255. Experi- 

 ments on the refranffibility of the invisible rays of the sun. p. 284. 

 Experiments on the solar and on the terrestrial rays that occa- 

 sion heat; with a comparative view of the laws to which light 

 and heat, or rather the rays which occasion them, are subject, in 

 order to determine whether they are the same or different, 

 pp. 293, 437. 



In connection with this inquiry, Sir William Herschel remarks, 

 that since a red glass stops no less than 692 out of 1,000 such 

 rays as are of the refrangibility of red light, we have a direct 

 and simple proof, in the case of the red glass, that the rays of 

 light are transmitted, while those of heat are stopped, and that 

 thus they have nothing in common but a certain equal degree of 

 refrangibility, which by the power of the glass must occasion 

 them to be thrown together into the place which is pointed out to 

 us by the visibility of the rays of light. 



On the same subject, a Memoir, by Sir Henry Erglefield, in 

 the Journal of the Royal Institution for 1802, p. 202, may 

 be consulted and Researches on Light, by the Author. 



