194 J. J. Woodward on Photo-micrography. 
been taken in the Army Medical Museum is a th, manufac- 
tured recently for the Museum by Messrs. Powell and Lealand of 
London. The subject selected for the experiment was Pleuro- 
sigma angulatum, ith the ,),th and three feet nine inches dis- 
tance and without an eye-piece, a picture of a portion of a frus- 
tule was obtained magnified 2,344 diameters. This negative 
readily bore enlargement to 19,050 diameters. The field in the 
About the same time experiments were made with the Wales’ 
$th, due amplification being given by the achromatic concave. 
It was intended to obtain with this the same power as with the 
- sth, but, although the distance was reduced to 8 feet, the subse- 
quent measurements showed 2,540 diameters, or about 200 diam- 
ings on Pleurosigma angulatum, an opinion which had previ- 
ously been expressed by Mr. Wenham. 
At the date of publication of Circular No. 6, Surgeon Gene- 
ral’s Office, both Dr. Curtis and myself believed these markings 
to be hexagonal, as was stated and figured on page 148 of that 
work. The greater power now obtained has corrected this opin- 
ion, but it is worthy of note that in the present pictures the 
markings appear hexagonal in both the small ones, if viewed 
with the eye at the visual distance, while on close inspection or 
with a lens they are seen to be circular. In the pictures with 
19,050 diameters the circular shape of the markings is very plain, 
t if viewed from a considerable distance or with a concave 
lens, they appear hexagonal. I also send you herewith a photo- 
graph of cartilage magnified 370 diameters, in illustration of the 
results attainable in the photography of the soft tissues. bh 
* On the evidence furnished by Photography as to the nature of the markings on 
the Pleurosigma angulatum ; by Prof. Q. N. Rood, this Journal, vol. xxxii, p. 335. 
