472 Intelligence and Miscellayieous Articles. 



agree with the formulae of M. Cauchy, to prove that the intensity of 

 metallic luminous reflexion depends on the colour of the light em- 

 ployed. The numerous analogies which exist between heat and 

 light, scarcely admit of an essential difference on this head. The 

 authors, indeed, are of opinion, that they have in fact proved by ex- 

 periment that this difference does not exist, and that the rays of heat 

 of different natures are reflected in very unequal proportions on the 

 same metallic mirror. 



The plan adopted and followed by the authors is precisely the 

 same as that previously followed in their Researches on Metallic 

 Reflectors. The source of heat was always a Locatelli's lamp ; 

 only they operated successively with the direct rays, and with the 

 same rays transmitted, sometimes through a plate of natural sal 

 gem, and at others with it smoked, and lastly through a lamina of 

 glass 5 millimetres in thickness. The incidence of the rays being 

 about 60°, the following results were obtained : — 



Experiments made with the Metal of the Reflectors of Telescopes . — 

 The metal of the reflector employed reflected 0*80 or 0-84 of the 

 direct heat of Locatelli's lamp. It reflected only 0*74 of the heat 

 derived from the same source when modified by passing through 

 a lamina of glass of 0"*005 in thickness. Lastly, it reflected 0'82 

 to 0*83 of the same heat transmitted through sal gem. 



Experiments with Silver. — The silver mirror reflected 0*95 to 0*9 6 

 of the natural heat, and 0*91 of the heat which had passed through 

 0-005 of glass. 



Experiments with Platina. — The platina employed reflected 0'79 

 of the natural heat; 0*77 to 0*78 of the heat which had traversed 

 sal gem ; 65 to 66 of that which had traversed 0'"'005 of glass ; and 

 lastly, 83 of that which had passed through smoked sal gem. 



Some experiments were also made with plates of gold and unpo- 

 lished silver, which were employed by the authors in an investiga- 

 tion respecting the diffusion of heat. The proportion of the incident 

 flow which these plates reflect back to the pole when it is placed in 

 the direction of the regular reflexion, is extremely different, according 

 as the heat has previously traversed glass or sal gem. 



It results from these numbers, that the heat most transmissible 

 through glass is reflected in smaller proportion on the various metals 

 tried ; and that the heat, which is transmitted in larger proportion 

 through smoked sal gem, is reflected more abundantly upon the 

 same substances. A marked consequence of these experiments is, 

 that a bundle of heat rays reflected on a metallic mirror has generally 

 a composition entirely different from that of the incident bundle, 

 and that consequently it should not suffer the same loss in traversing 

 diathermanous substances. This has been directly verified by the 

 authors in the following manner : — 



1. They determined the loss of intensity which the heat of a Lo- 

 catelli's lamp suffered in traversing a lamina of glass of O'^'OOS 

 in thickness. 



2. The loss suffered by heat from the same source twice reflected 

 on parallel mirrors. 



