66 Dr Stark on the Influence of Colour on Heat. 



a little more light. Blue and purple compared, the former 

 seemed to reflect a little more light. * Mr Boyle also found 

 that common burning glasses will not for a long time burn or 

 discolour white paper exposed to their action. When he was a 

 boy (he says) he took great pleasure in making experiments 

 with those glasses, and was much surprised at this remarkable 

 circumstance. He observed also, that the image of the sun was 

 not so well defined upon white paper as upon black ; and that 

 when he put ink upon the paper, so as to blacken its surface, 

 not only was the moisture quickly dried up, but the paper which 

 he could not burn before would presently take fire. Mr Boyle 

 also found, that, by exposing his hand to the sun with a black 

 glove upon it, it was suddenly and more considerably heated, 

 than if he held his naked hand to the rays, or put on a glove of 

 white leather. 



Mr Boyle, struck with these results, put the matter to the 

 test of further experiment. He took a large and broad tile, and 

 having coated one-half of its surface white and the other half 

 black, he exposed it to the rays of a summer sun. After expo- 

 sure for some time, he found, that while the whited part re- 

 mained cool, the portion that was black had grown very hot. 

 He further varied the experiment, by leaving part of the tile of 

 its native red ; and after exposing the whole to the sun for a 

 certain time, observed that this part grew hotter than the white, 

 but was not so hot as the hlach part. 



The same fact as to the absorption and reflexion of caloric 

 had been previously observed in regard to black and white mar- 

 ble ; and Mr Boyle relates, in further proof of its accuracy, that 

 a friend of unsuspected credit informed him, that in a hot cli- 

 mate, he had seen eggs well roasted in a short time, by first 

 blacking the shells, and then exposing them to the sun -|-. 



That indefatigable experimenter, Dr Hooke, afterwards re- 

 marked, that black and white marble being exposed equally to 

 the fire, the black will be found much hotter than the white, 

 because the white reflected back the rays which the other did 

 not ; and that a piece of white marble or stone, if one half of it 



• Bojle's Works by Birch, vol. i. p. 725. I.ond. 1772. 

 t Boyle's Works, vol. i. p. 70C-7. 



