17 2 DAGUERREOTYPES ARE DOTTED SURFACES. 



rope ; a number of the results were published in the American Journals during the 

 year 1837. In the detection of these lines I failed entirely ; but the bromuretted pa- 

 per enabled me, at that early period (while the attention of no other chemist was as 

 yet turned to these matters), to trace the blackening action from far beyond the 

 confines of the violet down almost to the other end of the spectrum. I distinctly 

 made out that the dark rays underwent interference after the manner of their luminous 

 companions, a result originally due to ARAGO, and printed some long papers in proof 

 of the physical independence of the chemical rays, and light, and heat, throughout the 

 spectrum. 



750. In a paper " On the Action of the Rays of the Solar Spectrum on the Da- 

 guerreotype Plate," inserted in the Philosophical Magazine for the month of February, 

 1843, which has just reached me, Sir JOHN HEKSCHEL points out that a connexion 

 may be traced between the phenomena of coloration impressed by the spectrum and 

 those of NEWTON'S rings. With striking ingenuity, he shows how a succession of pos- 

 itive and negative pictures may arise by prolonged solar action, and those shades of 

 colour which the iodide of silver exhibits, under variable exposure to light, originate. 



751. This hypothesis, however, as that able philosopher proceeds to state, is not 

 unattended with difficulties, and after pointing out what those difficulties are, he shows 

 how, nevertheless, it can account for an extensive group of facts. I regret that these 

 difficulties are in the way, and that there are also other facts which appear to ex- 

 clude the theory of thin plates from these phenomena. 



752. The Daguerreotype image, in all its forms, may be transferred by any copying 

 process to other suitable surfaces. In other words, it may be printed from. 



753. Sir DAVID BREWSTER was the first to show that the colours of mother-of-pearl 

 might be impressed on any yielding surface. In the same manner so can the Daguerre- 

 otype image. 



754. This is, unquestionably, the most important fact yet known in the history of 

 these mysterious images, both in a theoretical and in a practical point of view. In 

 a theoretical point of view, it shows us that it is among the phenomena of grooved, or 

 striated, or dotted surfaces that the Daguerreotype is to be ranged ; and, in a practical 

 point of view, it shows the true mode of solving the great problem of producing from 

 a given proof a multitude of copies. 



755. In (594), in speaking of the action of isinglass dried on the surface of the 

 Daguerreotype pictures, I stated that I had succeeded with a process for multiplying 

 copies, and promised on a future occasion to make it known : that promise I now pro- 

 ceed to redeem. 



756. On referring to the paper in question, the reader will perceive that the follow- 

 ing facts are stated (577) : that gum-arabic mucilage, dried on a common Daguerre- 

 otype, splits up, bringing with it the white portions ; that Russian isinglass, (584) and 

 (591), dried in a similar manner, does the same thing, and will even rend off the yel- 

 low coating of iodine if it has not be n previously removed. 



757. Now, in addition, I have to state that, if on a picture that has been fixed by a 

 film of gold, so as to be irremovable, a lay* r of isinglass be caused to dry and split up, 



