257 
as described in my memorandum, on the test Podura, a copy 
of which was previously sent. 
As the time of exposure required to make these pictures, 
was less than three minutes, I cannot agree with Mr. 
Wenham’s opinion that the object is seen by light reflected 
from above only. I believe on the contrary, that the scales 
being semi-transparent they are illumined chiefly by rays 
passing through them from below, and hence that the surface 
appearances are complicated by the optical properties of the 
structures beneath. 
The differences between the three pictures result simply 
from slight variations in the direction of the incident pencil 
of light, the position of the truncated lens and parabola 
being the same in all. 
Mr. P. T. AUSTEN gave an account of some investigations 
which he had recently made into the Comparative Merits of the 
various Methods proposed for the Analysis of Cinchona Bark. 
The gravimetric methods he found were almost without 
exception, tedious and unreliable. Special attention was 
given therefore to Glenard and Guillermond’s method, pub- 
lished by them in 1859, and modified in 1861. After describ- 
ing the process, the speaker remarked that some modifications 
were necessary to make it accurate. The standard of the 
author’s solution was incorrect, and an improved filtering corlk 
for drawing off the etherial solution was described. It was 
found best to use the bark in the condition of a moderately 
fine powder, and to employ slaked in preference to quick lime. 
With due regard to these precautions, this method was found 
to answer very well. Itindicates only the amount of Quinine 
it is true, but this is the principal measure of the value of 
the bark. It is rapidly executed, and gives results which 
agree very closley with each other. It can be specially 
recommended for commercial or technical analysis. The 
speaker next described a new salt of Quinine, formed by 
bringing together an Etherial solution of Quinine and an 
Alcoholic solution of Meconic acid. The salt, which is easily 
soluble in hot water, separates on cooling, in beautiful acicular 
