834 THE BEGINNINGS OF PHOTOGRAPHY. 



silver and its compounds, I commenced collecting- material for an 

 investigation into the evolution of photography with the salts of silver. 

 My attention was, however, diverted to the optical side of the ques- 

 tion connected with the history of the camera obscura and the 

 telephoto lens, and the results of those inquiries have been published 

 in the Journal. 



The publication of the late Mr. R. B. Litchfield's biography of Tom 

 Wedgwood, the first photographer, which was intended as a centenary 

 memoir of the founder of the art, has renewed my interest in the 

 subject, and the further investigations 1 have lately made have, I 

 think, thrown quite a new light upon the early histor}^ of photograph}^ 

 and .shown how it was gradually developed from Schulze's rough 

 experiment with silver nitrate and chalk, and finally brought about, 

 though imperfectly, by Wedgwood and Davy. This retrospect seems 

 the more opportune now that a century has passed since Wedgwood's 

 work was first made known, and we are about to celebrate the jubilee 

 of our societ}^ which, however, was not founded imtil after the iuA^en- 

 tion of collodion had put photographv on a thoroughly practical 

 basis. 



The main facts in the early history of the progress of photo-chem- 

 istry and optics tending to phc^tograph}' have been noted in • Prof. 

 J. M. Eder's admirable Ausfiihrliches Handbuch der Photographie 

 (Part I, 1891), in which I have found many useful references to the 

 early writers and literature. 1 know of no English work in which 

 the subject has been treated with the fullness it deserves. And this is 

 the more to be regretted because so much of the 6arly investigation 

 was done by Englishmen and is almost unknown. Robert Hunt's 

 Researches on Light has no pretensions to b(> a historv, while W. J. 

 Harrison's History of Photograph}', though it contains a short sum- 

 mary of the earl}^ work, is more devoted to the record of progress in 

 practical photography since 1S39. The story of these early experi- 

 ments is, however, an interesting one; and although I can only give a 

 brief and necessarilv very incomplete sketch of it, this ma}^ serve to 

 draw attention to the subject and incite further incpiir}'. 



EARLY NOTICES OF SALTS OF SILVER. 



Nitrate of silver seems to have been known from very early times. 

 Doctor Vogel infers from Herapath's statement that silver has been 

 found on linen niumm}^ cloths marked with hierogl3"phs that the 

 ancient Egyptians knew of the darkening action of light upon silver 

 nitrate. (W. and T. J. Herapath, Phil. Mag. (iv) 3, 528, and 5, 339.) 

 One of the earliest authentic accounts of it is given by Jabir i))n Hay- 

 yam (commonly Icnown as Geber), who lived about the seventh or 

 eighth century. Li the quaint English translations of his works by 

 Richard Russel (lt>78j we find a clear description of nitric acid (dis- 



