260 J. J. Woodward on Photographing 
No ground glass is used, but instead a lens mounted in a suitable 
tube is fixed in the opening of the shutter through which the 
solar pencil enters. This lens is an achromatic combination 
about two inches in transverse diameter and of about ten inches 
focal length. It is placed at such a distance from the achroma- 
tic condenser that the solar rays are brought to a focus and begin 
again to diverge before they reach the lowest glass of the 
achromatic condenser. 
For anatomical preparations requiring for their display from 
two to five hundred diameters, I use an 4th of an inch ob- 
jective, without an re a obtaining the precise power d 
by variations in the distance of the sensitive plate from the 
both neo aged as in the case of the ordinary solar micro 
scope. 
diameters obtained. While the object is thus seen on the white 
Screen in its natural colors, the cover corrections, focu: 
ussilg; , 
management of the achromatic condenser, and selection of the 
from about the microscope into the dark room; then going 
the plate holder, I make the final focussing in the usual way 
the ground glass, or on plate glass with the help of a focussilg 
glass, according to the nature of the object. 
- With powers of five hundred diameters or less, I at first & 
perienced some difficulty in giving the right exposure ; for 
the time required was buta fraction of a second, it was a na 
of some difficulty to regulate it with precision. At length. 
succeeded by arranging a sliding shutter, with a transverse 
of variable width, so adjusted as to fall with its own weiglt 
ache ine tube of ne microscope, the exposure being 
uring the passage, and the time of exposure re 
width given to the slit. <a 
/t course it occurred to me that for such short exposures = 
heliostat might bi 
be dispensed with, and I found on trial without 
