74 Dr Stark on the Influence of Colour on Heat. 



vi Four years previousto the appearance of Sir John Leslie's work, 

 and the Jater experiments of Count Ruraford, the investigations of 

 the late Sir William Herschel brought out some new facts regard- 

 ing the modification of heat by colour. This celebrated astrono- 

 mer, when viewing the sun through large telescopes by means of 

 differently coloured glasses, sometimes felt a strong sensation of 

 heat with very little light, and, at other times, a strong light 

 with little heat, — differences which appeared to depend on the 

 colour of the glasses used. This observation led to his researches 

 on the heating power of the prismatic colours, which were pub- 

 lished in the Philosophical Transactions for 1800. The experi- 

 ments made with a view to ascertain the heating power of the 

 different rays are detailed in the volume now referred to, and 

 afford very interesting results *. 



In this unsatisfactory state the subject of heat, as connected 

 with colour, was left. Subsequent inquirers seem to have 

 adopted the sentiments of Sir John Leslie, and regarded farther 

 inquiry as hopeless. Even Sir Humphry Davy, though he had 

 instituted an experiment with coloured pieces of metal similar to 

 that of Dr Franklin with coloured pieces of cloth, and ascertained 

 the comparative powers of different colours in absorbing heat, did 

 not pursue the subject further. He appears to have acquiesced 

 in the general idea, that the thing was incapable of being demon- 

 fitrated, though, in one of his works, he distinctly states it as 

 probable that the colour of bodies is connected with their power 

 of absorbing heat. " The manner (says he) in which the tem- 

 perature of bodies are affected by rays producing heat, is diffe- 

 rent for different substances, and is very much connected with 

 their colours. The bodies that absorb, as it is called, most light, 

 and of course that reflect least, are most heated when exposed 

 either to solar or terrestrial rays. Black bodies in general are 

 more heated than red ; red more than green ; green more than 

 yellow ; and yellow more than white. Metals are less heated 

 than earthy and stony bodies, or than animal and vegetable 

 matters. Polished surfaces are less heated than rough sur- 

 faces -f*."" 



The elementary writers on chemistry, since the date of Sir 



• Phil. Trans. 1800. 



+ Elements of Chemical Philosophy, vol. i. Lond. 1812. 



