~ 
366 J. J. Woodward on the Oxy-caleium Light 
The deviations of these values from the mean are perhaps due 
to errors of observation, especially in the determination of the 
densities, since in order to be sure of investigating the same 
material as in the original experiments, but small masses could 
be employed. It is possible too that the deviation of the mean 
from the whole number 6, is to be sought in these errors. 
Without entering on a more extended investigation of this 
point, and without discussion as to whether the customary 
theory of elasticity is applicable to such thin wires, or whether 
the lack of isotropy, or the relations of superficies, forbid this 
application, it may be remarked that according to the theory 
A 
iT — 4(i+u ), 
where u denotes the ratio of the transversal contraction to the 
longitudinal dilatation. a comparison of the torsional and 
1 
=6 there results u=4. This is the extreme value 
permitted by the theory, which would correspond to a volume 
unchanged by dilatation. ; 
It may suffice to have indicated the fact. It would lead us 
too far from the chief object of our investigation to develope 
the subject more in detai 
E 
- 
a 
z 
he 
Art. XXXVIIL—On the Oxy-Caleium Light as applied to Photo- 
Micrography ; by Lieut. Col. J. J. Woopwarp, Assistant Sur- 
geon, U. S. Army. Report to the Surgeon General of the 
U.S. Army, dated June 4, 1870. 
_ Since the preparation of my report of January 4, 1870, on the 
use of the Magnesium and Electric lights in Photo-micrography, 
I have made some experiments with the Oxy-calcium, or Hare’s 
light, as a source of illumination for the same purpose, and have 
succeeded in obtaining excellent pictures with powers as high 
as a thousand diameters. is result appears to me of consid- 
erable Pree both because of the comparative cheapness 
of this light, and because the apparatus for its production 1s S0 
common as to be practically within the sack 
