90 
NOTES AND MEMOEANDA. 
" Dr. Hunt, having thus washed his hands of this most curious 
report, makes a novel and startling proposition, ' the object heing to test 
men in regard to their technological skill.' This is a brilliant idea 
and to the point— rather ominous for the committee however ! " 
Angle of Aperture. — Mr. E. B. ToUes writes thus in the ' Cin- 
cinnati Medical News ' (June, 1875) : — " ' Mr. Wenham is unquestion- 
ably right in stating that if an isosceles triangle be described, the base 
of which is ten times the measured diameter of the front lens, and the 
altitude ten times the measured distance of the focal point from the 
same surface, the vertical angle of that triangle will correctly repre- 
sent the maximum available aperture.' * 
" Taken as stated here by Mr. Brooke, the rule proves contra- 
dictory. Thus, Mr. Wenham gives the focus of the objective he 
measured! as '013 of an inch i7i air. Diameter of front surface 
•043 of an inch. From these data he deduces that 118° is the 
maximum angle possible in the case from plain measurement, &c. But 
Mr. Brooke says, the rule gives ' the maximum available aperture.' 
Apply this rule, then, to get the aperture in ' balsam.' 
" Here are the data : Mr. Wenham, in the ' Monthly Microscopical 
Journal ' for May, 1875, p. 225, gives the focus in balsam as 0*018 of 
an inch. Thus we have the elements for the triangle in balsam. 
Applying the rule we get a ' vertical angle ' of 88°. But 82° in 
' balsam ' is equivalent to (infinitely near) 180° of pencil entering or 
emerging at a plane surface. Consequently their rule with Mr. 
Wenham's own data, viz. diameter 0*043, median height 0*018, 
proves the objective he declared J could not by any possibility have 
more than 118° of aperture, has, by the same rule, all the air-angle, 
i. e. angle for a dry mount, that any objective possibly can have." 
How to Prepare the Biatomacese. — Herr J. D. Moller proposes 
to publish a work on this subject, and has offered the following as the 
plan on which it will be issued : " To the undersigned was repeatedly 
expressed the wish : to publish his procedure to prepare Diatomaceae. 
He declares himself ready to do it for a corresponding indemnifica- 
tion, and has the intention to try the following. If a number of sub- 
scribers is obtained, he will publish a little work with illustrations, 
which will have the title ' The Preparation of the Diatomaceae,' and 
which will contain : 1. The collecting ; 2. The cleaning and purify- 
ing (a) of the living subjects, (b) of dead subjects in the mud, (c) of 
fossils. 3. The separation of the different species. 4. The prepara- 
tion and mounting, (a) in the ordinary manner (in quantity), (b) as 
selected and arranged, (c) as ' Typen- and Probe-Platte,' &c. Price 
for the German edition, 30 marks ; English, 11. 12s.; French, 40 francs. 
Besides the undersigned, the following gentlemen will kindly receive 
orders : G. F. Otto Miiller, Koniggratzer Str. 21, Berlin W. ; Dr. E. 
Hartnack and A. Prazmowsky, Kue Bonaparte, 1, Paris ; E. and J. 
Beck, 31, Cornhill, London, E.C.; Edmund Wheeler, 48, ToUington 
* From the Annual AddieisS of President Charles Brooke before the Royal 
Microscopical Society, London, February, 1875. 
t ' M. M. J.,' March, 1874, p. 114. 
X Ibid. 
