the Deposition of Dew ^ and on Odours. 83 



board covered with paper blackened with ink. At daylight,""' 

 says he, " I observed hoar-frost upon both pieces, but the black 

 seemed to have a greater quantity than the white."" ♦ 



These facts, it might have been supposed, would have led 

 Dr Wells to further experiments with different colours. But 

 the reverse was the case. He quotes Mr Leslie as to the hope- 

 lessness of success, without making a farther attempt ; '' since a 

 black body almost always differs from a white one in one or 

 more chemical properties, and this difference may alone be suffi- 

 cient to occasion a diversity in their powers of radiating h^at."" 



IV. — On the Influence of Colour on Odours. 



If the influence of colour over heat attracted but little the 

 attention of philosophers employed in the investigation of the 

 absorbing and radiating powers of different substances, even 

 when presented to their notice in anomalous facts, which could 

 not easily be explained on any other principle, it is not to be 

 wondered at, that the apparently far less appreciable influence 

 of colour on odours should have totally escaped notice. In 

 point of fact, I am not aware that the subject has hitherto been 

 investigated, and know of no recorded facts in which the in- 

 fluence of colour over odours has been pointed out. In at- 

 tempting to shew from experiment, that the colour of bodies in 

 imbibing odours is correlative with the power of colour over the 

 absorption and radiation of heat, I state a fact, which, though 

 new to science, is in admirable correspondence with the known 

 properties of light and heat. And though I may not be able, 

 from the nature of the substances subjected to experiment, ab- 

 solutely to determine the amount of this connexion, I trust my 

 imperfect investigations may form the basis of new and better 

 devised experiments, by directing the attention of men of science 

 to this hitherto untrodden field of inquiry. 



Odour is that quality of bodies which is distinguished by the 

 sense of smell. This sense is nearly connected with that of taste ; 

 so much so, indeed, that they have sometimes been considered 

 as modifications of the same sensation. It has been remarked, 

 that what is agreeable to the olfactory organs, is in general a 

 • Wells on Dew, p. 106. Lond. 1814. 



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