52 
PROCEEDINGS OF SOCIETIES. 
ment, page 95, is, to say the least, rather coloured and fanciful, and 
that I was perfectly right, indignantly to turn my back to him after 
such a result, he even trying to abuse M. Hartnack and others. 
Yours most devotedly, 
Dr. Leopold Dippel, 
Professor in Ordinary of Botany, 
Angle of Aperture. 
To the Editor of the ' Monthly Microscopical Journal.'' 
Sir, — In anticipation of the reformed list of apertures of micro- 
scope objectives that I believe will be required, I may recommend 
microscopists, as an adjunct with the sector, to try their present aper- 
tures by means of a micrometer measurement of the diameter of the 
luminous spot, or working portion of the front lens ; taking this as 
a base, and the distance of the focus as a height, for the angle. This 
is easily accomplished with the ordinary means at hand. 
It seems a forlorn act for Mr. ToUes to ignore my measurements, 
and send others across the Atlantic in place of them. His case has 
at length collapsed. I had not before the last revival of the ques- 
tion that confirmed this conclusion measured the portion of the true 
tvorhing diameter of the front lens ( • 033) or the exact distance of 
the immersed focus ('025) corrected for an object actually mounted in 
balsam. These measurements I can show so plainly and unmistakably, 
that no unprejudiced person can for one moment doubt them. 
I am. Sir, yours truly, 
F. H. Wenham. 
PEOCEEDINGS OF SOCIETIES. 
EoYAL Microscopical Society. 
King's College, June 7, 1876. 
In the absence of the President and Vice-Presidents, the chair was 
taken by Mr. H. J. Slack, on the motion of Mr. J. W. Stephenson, 
seconded by Mr. J. C. Sigsworth. 
The minutes of the preceding meeting were read and confirmed. 
A list of donations to the Society was read, and the thanks of the 
meeting were voted to the donors. 
The Chairman called attention to a donation from Mr. Hanks, of 
San Francisco, consisting of some diatomaceous earth from Santa 
Monica, near Los Angelos, and which seemed to be very rich in 
various circular forms. Some slides of diatoms from this material 
had been prepared by Mr. Barnett, and were upon the table for 
examination. 
