140 ANNUAL OF SCIENTIFIC DISCOVERY. 



THE PHENOMENA OF THE DAGUERREOTTPE PROCESS. 



M. CLATJDET has communicated to the British Association a paper 

 " On Researches on the Theory of the principal Phenomena of Photog- 

 raphy in the Daguerreotype Process." Light produces two differ- 

 ent effects on the Daguerreotype plate, capable of giving an image. 

 By one, the surface is decomposed, and the silver is precipitated as a 

 white powder; this action is very slow. By the other, the parts 

 affected by light receive an affinity for the mercurial vapor, and this 

 metal is deposited in white crystals. This action, which is the cause 

 of the Daguerreotype image, is 3,000 times more rapid than the for- 

 mer. The two cannot proceed from the same cause. The first is a 

 chemical decomposition of the surface, while the second is a new prop- 

 erty imparted to the surface to attract the vapor of mercury, which 

 is given by some rays and withdrawn by others, the most refrangible 

 rays being the ones which produce the affinity for mercury. M. 

 Claudet has so improved his photographometer that he can compose 

 upon the same plate a series of intensities in a geometrical progres- 

 sion, varying from 1 to 512, or by employing two plates at the same 

 moment," from 1 to 8,192. He is also enabled to study the modifica- 

 tions produced on various intensities of effect by the radiation of half 

 the light, through various colored glasses. M. Ciaudet has ascertained 

 one remarkable and inexplicable fact, that the two foci for the same 

 distance of an object sometimes coincide and sometimes vary very far 

 from one another ; and the difference varies according to some un- 

 known properties of the lenses, so that while the foci correspond in 

 some lenses, they may be separated in others. London Athenccum, 

 Sept. 



COLORED PHOTOGRAPHS. 



THE Comptes Rendus, of the 12th February, contains the report 

 of M. Biot and others, on the process discovered by M. Becquerel, of 

 making photographic copies of colored objects with distinct impres- 

 sions of the colors on the body so copied. The prospect, however 

 remote at present, of being able to copy Nature in all the truth of 

 color, gives great interest to every experiment which leads to an 

 advance in this particular. The main features of the new process 

 are the following. The ordinary silver plate, well polished, is con- 

 nected with the positive pole of a battery of two series, and then 

 plunged into a large vessel containing diluted hydrochloric acid. In 

 the same fluid is placed a third plate of platina, which communicates 

 with the negative of the battery. This plate is brought very rapidly 

 a short distance from and parallel to the other. Under these condi- 

 tions, the plate assumes successively the colors of thin films; at first a 

 gray, then a yellow and violet tint, which passes soon to a blue and 

 to a green, and becomes afterwards rose-colored, then violet, and at 

 last blue. The operation must be stopped as soon as a lilac tint ap- 

 pears, and the plate withdrawn rapidly from the bath, washed with 

 distilled water, and being placed in an inclined position, dried over a 



