284 Proceedings of the British Association for 1850. 



brought to such perfection in this city by Messrs Ross and 

 Thompson, that Talbotypes taken by them, and lately ex- 

 hibited by myself to the National Institute of France, and to 

 M. Niepce, were universally regarded as the finest that had 

 yet been executed. Another process, in which gelatine is 

 substituted for albumen, has been invented, and successfully 

 practised by M. Poitevin, a French officer of engineers, and 

 by an ingenious method, which has been minutely described 

 in the weekly proceedings of the Institute of France, M. Ed- 

 mund Becquerel has succeeded in transferring to a Daguer- 

 reotype plate the prismatic spectrum, with all its brilliant 

 colour, and also, though in an inferior degree, the colours 

 of the landscape. These colours, however, are very fugace- 

 ous : yet, though no method of fixing them has yet been dis- 

 covered, we cannot doubt that the difficulty will be sur- 

 mounted, and that we shall yet see all the colours of the na- 

 tural world transferred by their own rays to surfaces both of 

 silver and paper. But the most important fact in Photo- 

 graphy which I have now to mention, is the singular accele- 

 ration of the process discovered by M. Niepce, which enables 

 him to take the picture of a landscape, illuminated by diffused 

 light, in a single second, or at most in two seconds. By this 

 process he obtained a picture of the sun on albumen so in- 

 stantaneously, as to confirm the remarkable discovery, pre- 

 viously made by M. Arago, by means of a silver plate, that 

 the rays which proceed from the central parts of the sun's 

 disc, have a higher photogenic action than those which issue 

 from its margin. This interesting discovery of M. Arago is 

 one of a series on photometry, which that distinguished 

 philosopher is now occupied in publishing. Threatened with 

 a calamity which the civilized world will deplore — the loss 

 of that sight which has detected so many brilliant pheno- 

 mena, and penetrated so deeply the mysteries of the material 

 world, he is now completing, with the aid of other eyes than 

 his own, those splendid researches which will immortalize 

 his own name and add to the scientific glory of his country. 

 From these brief notices of the progress of science, I must 

 now call your attention to two important objects with which 

 the British Association has been occupied since their last 

 meeting. It has been long known, both from theory and in 



