2O ELEMENTARY PHOTO-MICROGRAPHY. 



The adaptability of a quarter-plate camera for 

 all purposes may be seen from the fact that any- 

 thing from the smallest bacteria, or the most 

 difficult test diatom, to a five-shilling piece, in 

 fact anything within the range of a microscope, 

 may be taken with a camera extension varying 

 from 3in. to loin. Moreover, it is desirable that 

 the worker should have the whole of his apparatus 

 within easy reach during the operations of centring, 

 illuminating, and focussing the specimen without 

 change of position, and with long camera extension 

 this is not possible. 



The whole of the processes hereinafter described 

 are intended to be carried out by artificial light. 



There is a difference betwixt the visual and the 

 actinic foci, and objectives corrected for photo- 

 graphy are sold, but ordinary objectives made by 

 good firms give results not to be despised. Even 

 with high powers tolerable negatives can be 

 obtained, and the brain work of a practical mani- 

 pulator will often compensate for lack of expensive 

 apparatus. 



USE OF EYEPIECES. 



The use of eyepieces is condemned by some 

 writers without much reason. If the eyepiece be 

 not used, a long extension of camera is needed, 

 whereby the apparatus becomes troublesome, and 

 the result is not one jot better than when the eye- 

 piece is employed. The loss of light occasioned by 



