[201] 



^be application of pbotoorapbi? to tbe 

 delineation of fIDieroacopic ©bjecte* 



By William Pumphrey. 



A Paper read before the Members of the Bath 

 Microscopical Society. 



THE subject of the present paper may, perhaps, be thought 

 hardly fit to engage the attention of the microscopist, 

 seeing that it can never supplant the study of natural 

 objects by the eye of the observer through the microscope. Photo- 

 micrography can never become a means of exact scientific research, 

 but must be reserved for the more popular display of microscopic 

 objects, or as a help towards their more accurate delineation. The 

 difficulty of obtaining really good and reliable drawings of such 

 objects must make any easily available plan for giving us such 

 copies a desideratum^ and if such a plan does not at once give us all 

 that we desire, it is a fault belonging alike to other things, even to 

 those which are capable of the utmost advance towards perfection. 

 The application of Photography to the delineation of micro- 

 scopic objects is, at the present day, very far from being a novelty. 

 So far as I am aware, the earliest photo-micrographs were pro- 

 duced about the year 185 1, on silver plates, prepared after the 

 process of Daguerre, and those who know anything of the 

 difficulties attending that process would be surprised that any really 

 valuable results could have been obtained by it. The introduc- 

 tion of a film of collodion, as a vehicle for exhibiting the haloid 

 salts of silver to the action of light, greatly facilitated the produc- 

 tion of good photo-micrographs. This photographic process had, 

 however, one great disadvantage, viz. — the sensitive surface was a 

 moist one, and as, in consequence of the great dispersion of the 

 light, a very long exposure was often required to obtain a sufficiently 

 vigorous impression, the surface of the prepared plate became dry 

 during the exposure, and the result was that the luminous impres- 

 sion was unequal in different parts of the plate, and the picture 

 being uneven was rendered comparatively valueless. 



