190 



PHO TO MICROGRAPHY. 



[CH. VIII. 



arisen from differences in the foci. This is especially true when mono-chro- 

 matic light and even when petroleum light is used. In case the two foci are so 

 unlike in an objective, it would be better to discard it for photography altogether, 

 for the estimation of the prooer position of the sensitive plate after focusing is 

 only guess work and the result is only mere chance. If sharp pictures cannot be 

 obtained with an objective when lamp light and orthochromatic plates are used 

 the fault may not rest with the objective but with the plate holder and focusing 



Fig. 14') Walmstey's Autograph Photo-Micrograpkic Camera in a vertical po- 

 sition. Compare Fig. 1 /? ( From the Proc. Amer. Micr. Soc. Vol. A VII, tSgs). 



