Dr Stark o?i i?ie Influence of Colour on Heat. 67 



was coloured black, wouW, when exposed to the fire, be much 

 hotter on the black part than on the white *. 



The subject of light and colours was now taken up by the 

 greatest of names in modern science, Sir Isaac Newton. His 

 discoveries were communicated to the Royal Society in a letter 

 early in the year 1672. He had ascertained by experiments with 

 the prism, that a beam of white light, as emitted from the sun, 

 consists of several different colours, which possess different de- 

 grees of refrangibility. These primary and simple colours are 

 red^ orange, yellow, green, blue, indigo, and violet He ob- 

 served that the red was refracted least, and the violet most 

 powerfully ; and was thence led to the conclusion, that the same 

 degree of refrangibility always belonged to the same colour, and 

 the same colour to the same degree of refrangibility ; that white- 

 nessor white light is a compoundof all the colours of the spectrum; 

 that blackness was a privation of all colour; and that the colours of 

 natural bodies are not qualities inherent in the bodies them- 

 selves, but arise from the disposition of the particles of each 

 body to stop or absorb certain rays, and thus to reflect more 

 copiously those rays which are not absorbed. 



As my object, however, is not the investigation of the abstract 

 nature of colours, or their production, as connected with light, 

 but only to trace some of the modifications which coloured 

 bodies, as they exist in nature, or are produced by art, exert 

 over heat, I leave, for the present, the brilliant experiments of 

 Newton. As connected, however, with Sir Isaac**s analysis, 

 it may be mentioned, that Sir David Brewster has very re- 

 cently discovered that the prismatic spectrum consists of three 

 different spectra, viz. red, yellow, and blue, all having the same 

 length, and all overlying each other ; and that the seven as- 

 sumed colours are all compounded of these three simple and 

 primary onesf. 



The more immediate subject of these observations was now 

 taken up by the celebrated Dr Franklin, who seems to have re- 

 peated most of Boyle's experiments, and detailed the results 

 in a letter to a friend in 1761. He observed that different parts 

 of dress, coloured black and white, imbibe the rays in different 



• Birch's History of the Royal Society, vol. iv. p. 175. 

 f Edin. Trans, vol. xii. p. 123. 



e2 



