as applied to Photo-micrography. 367 
The oxygen was sometimes made in the usual way from 
chlorate of potassa, sometimes purchased compressed in iron 
cylinders ; in either case it was transferred to a large sheet-iron 
gasometer for use. The gases were burned under a pressure 
equal to a column of water fourteen inches high. I used for 
lamp one of the first-class magic-lanterns, manufactured by 
J. W. Queen & Co. (No. 924, Chestnut street, Philadelphia, 
Pennsylvania,) in which the disc of lime is revolved by clock- 
work before the burning jet of gas and a fresh surface con- 
stantly presented to the flame. I simply removed from the 
lantern the lens intended to magnify the image on the slides, 
when the apparatus is in ordinary use, and allowed the cone of 
the magnesium lamp, does not produce the interference phe- 
nomena which result when tissues and many other objects are 
illuminated by powerful parallel rays. This circumstance, how- 
ever, renders the calcium light inferior to the sun and the elec- 
tric lamp, in the resolution of the Nobert’s plate and certain 
lined test objects. 
I did not find the time of x ee differed materially from 
Oo 
of obtaining positive information with regard to the comparative 
Moved the 
was itt 
peel mines portion of a sensitive plate thirty feet distant. 
