268 M. Melioni on Uie Radiations of Incandescent Bodies, 



The numbers of the two latter columns show evidently that 

 the augmentations of both these agents, though feeble at first, 

 become very rapid at last; from which it results that the ra- 

 diations both of light and heat follow in the jn'ogression of 

 quantity the same analogy that we have just observed in the 

 "progression of qiialitij. 



This parallel march of the two agents seems to have entirely 

 changed the opinion of the author as to the nature of the rays 

 of light and heat, and the different chemical and physiological 

 effects due to the sun and terrestrial luminous and calorific 

 sources. The preamble of his memoir contains the following 

 passage relative to this point : — 



" As the experiments now to be described lead to some 

 striking and perhaps unexpected analogies between light and 

 heat, they commend themselves to our attention, as having a 

 bearing on the question of the identity of those imponderable 

 principles. It is known that heretofore I have been led to 

 beheve in the existence of cardinal distinctions, not only be- 

 tween these but also other imponderable agents; and 1 may 

 therefore state, that when this investigation was first under- 

 taken, it was in the expectation that it would lead to results 

 very different from those that have actually arisen." 



The author adds, immediately after the experiments relative 

 to the luminous and calorific radiations, which are simultane- 

 ously developed in the strip of platina at different phases of 

 incandescence, " I cannot here express myself with too much 

 emphasis on the remarkable analogy between light and heat 

 which these experiments reveal. The march of the phaeno- 

 mena, in all their leading points, is the same in both cases. 

 The rapid increase of effect as the temperature rises is common 

 to both. And it is not to be forgotten, that, in the case of 

 light, we necessarily measure its effects by an apparatus which 

 possesses special peculiarities. The eye is insensible to rays 

 which are not comprehended within certain limits of refrangi- 

 bility. In these experiments, it is requisite to raise the tem- 

 perature of the platinum almost to 1000° before we can dis- 

 cover the first traces of light. Measures obtained under such 

 circumstances are dependent on the physiological action of 

 the visual organ itself, and hence their analogy with those 

 obtained by the thermometer becomes more striking, because 

 we should scarcely have anticipated that it could be so com- 

 plete." 



After the second series of experiments, relative to the qua- 

 lity of the rays emitted as the temperature of the metal rises, 

 Professor Draper criticises some of the facts upon which Sir 

 D. Brewster founds his opinion on the existence of the red, 

 yellow, and blue colours in every part of the Newtonian spec- 



