178 ANNUAL OF SCIENTIFIC DISCOVERY. 



Improvement in the Collodion Process. The great difficulty with this most 

 sensitive process has been the rapid loss of sensibility after the plate has been 

 properly excited. This has arisen from the rapidity with which the ether and 

 alcohol of the collodion are removed by evaporation. Messrs. Spiller & Crookes 

 of London, have adopted the following method, which seems to overcome the 

 difficulty in question : After the collodion plate has been fully prepared in the 

 usual manner, it is placed in a bath of nitrate of zinc containing a small 

 quantity of nitrate of silver. In a few minutes it absorbs a sufficient quantity 

 of this salt to- secure a long-continued moisture on the surface ; and thus 

 plates which have been prepared for five days have retained a sensibility equal 

 to that which they possess, under ordinary circumstances, for five minutes. 



Photography and Wood Engraving. Mr. R. Langton, wood-engraver and 

 draughtsman, of Manchester, has produced some very successful and beautiful 

 specimens of photography, taken by himself, on blocks of bos- wood. This 

 photograph, so taken, is quite ready for the application of the wood-engraver's 

 burin. It is impossible to say how greatly this will advance the process of 

 wood-engraving, especially by saving all the preliminary labor of the draughts- 

 man ; which, in many cases, constitutes the chief element in both the time 

 and the cost attendant on the production of wood-engravings of a high class. 

 Even in many of the lower branches of the art, the new application of sun- 

 drawing will be an invaluable auxiliary. For instance, it is an exceedingly 

 difficult matter to get accurate drawings of machinery in perspective ; me- 

 chanical draughtsmen only represent it in plane ; and artists are generally 

 found extremely reluctant to employ a large amount of time so unprofitably 

 as the drawing of a complicated machine in perspective demands. These 

 photographs can now, in a few seconds, accomplish what it would require 

 hours for the artist to effect , and in point of accuracy the instrument must 

 ever have the preference. But great as will eventually be the boon which 

 this new application of photography will confer on the practical art of wood- 

 engraving, it may be made more extensively valuable as a cheap form of 

 producing pictorial objects. By Mr. Langton's process, portraits, landscapes, 

 etc., could be produced on any smooth piece of wood, duly prepared ; and 

 thus even wooden snuff-boxes, hand-screens, etc., may be decorated with por- 

 traits, or scenes from nature, or copies of works of art, at a cost much less 

 than daguerreotypes on metal plates. Indeed, it is difficult to say where the 

 application and uses of this new process may extend. The inventor does not 

 limit his invention to its use in wood-engraving, but claims for it an equally 

 valuable application in other directions, in connection with practical art. Civil 

 Engineer and Architect's Journal. 



Duration of Photographs. What is the average duration of a photograph or 

 daguerreotype ? Is their longevity in a ratio with the period of time of their 

 production, or is their existence's length determined by other elements ? In 

 these matters, time is the only possible CEdipus. But some photographs last 

 longer than others, and some have already faded away from the sensitive plate. 

 It seems, however, these may be recalled (according to MM. Davanne and 

 Girard) by a salt of gold, but with different aspects and shades, which go 

 from red to black and blue; there being a. coaipvx reaction, vi/., a pro- 



