242 THE LIFE OF JAMES D. FORBES. [CHAP 



of the day fixed in three or four minutes, including the 

 most exquisitely delicate objects, and giving the shadows 

 proper to the time of day in a way no artist can do. 

 .... Arago repeated several times Herschel's remark 

 on seeing them : " Nous ne sommes que des barbouilleurs 

 on n'aurait pas pu s'en former une ide'e. C'est admir- 

 able ! c'est une miracle ! " 



* Afterwards I spent some hours with M. Babinet and 

 his friend M. Moigno, and was agreeably surprised to 

 find him well acquainted with my experiments on heat, 

 as well as to find that he had formed a just estimation 

 of Melloni's claims to his discoveries in polarization. 

 I showed him my method of making polarizing plates 

 of mica, a process which I afterwards explained to 

 Lerebours the optician, leaving with him some speci- 

 mens, and then visited M. Cauchy, who received me 

 with great politeness and explained very clearly his 



views on the laws of reflection of light on metals 



I gave him a reference to MacCullogh's memorandum, 

 which he did not know, and he expressed great interest 

 in the subject of heat, seeming much pleased by the 

 account I gave him of my own experiments/ 



Journal, May 17. 



' M. Elie de Beaumont called in the morning, when 

 I gave him my results of two years' computations of the 

 conductivity of soils. ... I afterwards called on M. 

 Isidore Niepce, who had the week before showed me the 

 first specimens of the Daguerre process, as discovered by 

 his father M. Niepce, and whom I found a most gentle- 

 manly person. He explained the process circumstan- 

 tially, and I have no doubt correctly. 



' I examined the pictures very minutely. The substance 

 is acknowledged to be silver, plated on copper, and Arago 

 suspected that the metals produced some galvanic effect, 

 but it is evident that the surface has most to do with it. 

 .... The pictures of both Niepce and Daguerre have 

 this very singular peculiarity, that the parts which are 

 dark, and therefore unaltered, have an aspect simply 



