Dr Stark on the Influence of^ Colour 07t Heat. 75 



Humphry Davy's work, merely mention the subject in similar 

 terms to his ; and even Dr Edward Turner, one of the latest 

 and most acute chemical investigators, remarks, ** that the ab- 

 sorption of luminous caloric, whether proceeding from the sun 

 or a common fire, is very much influenced by colour ; it is most 

 considerable in black and dark coloured surfaces, while it is much 

 less in white ones. The influence of colour, on the contrary, 

 in the absorption of non-luminous caloric, is exceedingly slight : 

 it remains to be proved indeed whether any effect can be fairly 

 attributed to this cause. *"" 



Such is the present state of our knowledge of the influence of 

 colour upon the absorption and radiation of heat. The influence 

 of colour, at least of a black surface, though noticed by Boyle, 

 Dr Watson, and more lately by Count Rumford, and remarked 

 as an unaccountable circumstance in his results, failed to induce 

 that active experimentalist to make a trial of other colours. Sir 

 John Leslie was equally surprised at the result of a nearly 

 simultaneous experiment of the same nature, which he supposed 

 not to have been before observed, and remarks, not only that it 

 is contrary to the prevalent notions on the subject, but that the 

 question is incapable of being resolved. Dr Thomas Thomson, 

 in his late work, says, that " hitherto it has been impossible to 

 ascertain the efficacy of hardness and softness, or of colour, upon 

 the radiation of heat -f ."" 



I am far from thinking that the experiments I have made :j: 

 will solve all the phenomena observed, where colour may be sup- 

 posed to influence the results. All I maintain is, that colour ex- 

 erts a powerful influence over the absorption and radiation of 

 caloric, either luminous or non-luminous. Future experiments 

 may determine the extent of this modifying principle, which, till 

 now, has been doubted or denied by most of the writers who 

 have alluded to the subject. 



I. — On the Absorption of Heat by differently Coloured Substances. 



My first experiments were made with wool variously coloured, 

 and as nearly as possible of the same degree of fineness. These 



* Elements of Chemistry, fourth ed. p. 18. 



t An Outline of the Sciences of Heat and Electricity. Lond. 1830, p. 147. 



X See Phil. Trans. 1833, p. 285. et seq. 



