Photography in the Daguerreotype Process. 381 



electric current. May we not hope that the conditions 

 being known in which the action is produced, and by avail- 

 ing ourselves of that property, it will be possible to increase 

 on the Daguerreotype plate the action of light ? for it is not 

 improbable that the affinity for mercury imparted to the plate 

 is also due to some electrical influence of light. How could we 

 otherwise explain that affinity for mercury given by some rays 

 and withdrawn by some others, long before light has acted as 

 a chemical agent? 



Photography is certainly one of the most important disco- 

 veries of our age. In relation to physics and chemistry, it has 

 already been the means of elucidating many points which had 

 not been investigated, or which were imperfectly known before. 

 We may certainly expect that its study will prove of consider- 

 able use to the progress of these sciences. But it is in reference 

 to optics that it opens a large field for research and discovery. 

 Had Newton been acquainted with the properties with which 

 light is endowed in the phaenomena of photography, there is 

 no doubt he would have left a more complete theory of light, 

 and of the various rays which compose it. 



Since the discovery of photography, opticians have turned 

 their attention to the constructing of new combinations of 

 lenses, in order to increase the illuminating power without 

 augmenting the aberration of sphericity. It is due to justice 

 to state here, that the optician who first produced the best 

 lenses for photography is M, Voigtlander of Vienna, and they 

 still are the most perfect that a photographer can use, parti- 

 cularly for portraits. In this country an optician of great 

 merit, Mr. A. Ross, has constructed lenses on similar prin- 

 ciples; and at all events has succeeded in producing some 

 which work as quick, and give an image as perfect in every 

 respect. In Paris M. Lerebours is renowned for lenses with 

 larger focus, which are better adapted for taking views than 

 any I have tried. 



From the beginning of photography it was well known that 

 the effective rays being the most refrangible, had a shorter 

 focus than those producing white light; and for this reason 

 Daguerre himself recommended the use of achromatic lenses, 

 in which all the rays were supposed to coincide nearly at the 

 same focus. All camerae obscura3 were furnished with achro- 

 matic lenses, and constructed so that the plate could be placed 

 exactly at the same distance as the ground glass on which the 

 image had appeared the best defined. But with these cameras 

 obscurae it was very difficult to obtain a photographic image 

 so perfect as that seen on the ground glass ; and it was only 

 now and then, and as if by accident, that good pictures could 

 be produced. 



