62 ADDRESS TO THE BRITISH ASSOCIATION, 1881. 



Another remarkable triumph of the last half- century 

 has been the discovery of photography. At the com- 

 mencement of the century Wedgwood and Davy ob- 

 served the effect produced by throwing the images of 

 objects on paper or leather prepared with nitrate of 

 silver, but no means were known by which such images 

 could be fixed. This was first effected by Niepce, but 

 his processes were open to objections, which prevented 

 them from coming into general use, and it was not till 

 1839 that Daguerre invented the process which was 

 justly named after him. Very soon a further improve- 

 ment was effected by our countryman Talbot. He not 

 only fixed his ' Talbotypes ' on paper in itself a great 

 convenience but, by obtaining a negative, rendered it 

 possible to take off any number of positive, or natural, 

 copies from one original picture. This process is the 

 foundation of all the methods now in use ; perhaps the 

 greatest improvements having been the use of glass 

 plates, first proposed by Sir John Herschel ; of collodion, 

 suggested by Le Grey, and practically used by Archer ; 

 and, more lately, of gelatine, the foundation of the 

 sensitive film now growing into general use in the 

 ordinary dry-plate process. Not only have a great 

 variety of other beautiful processes been invented, but 

 the delicacy of the sensitive film has been immensely 

 increased, with the advantage, among others, of diminish- 

 ing greatly the time necessary for obtaining a picture, 

 so that even an express train going at full speed can 

 now be taken. Indeed, with full sunlight g-i^ of a 

 second is enough, and in photographing the sun itself 



of a second is sufficient. 

 We owe to Wheatstone the conception that the idea 



