1876.J Microscopy. 425 
used in centreing the condenser consisted of an accurately centred diaphragm 
beneath the optical portion, having an aperture of not more than the ninetieth 
or hundredth of an inch : by means of the adjusting screws the image of this 
aperture is brought carefully to the centre of the field of a moderate power. 
If the illuminating pencil be now carefully manipulated, and the i-5oth ob- 
jective be put on, it will be found that the image can be brought to a focus 
presenting a central disc of light with a margin of the black diaphragm. By 
an accidental movement of the mirror Mr. Dallinger found that this minute 
spot of light might be spread over the entire field, presenting a disc, with an 
intense minute speck in the centre, with an equal diffusion of rays all round, 
excepting that the illumination grows uniformly less as it reaches the margin 
of the field. This light was found to be extremely favourable for the display 
of minute detail under such high powers as the i-25th and i-5oth. The diffi- 
culty in using this mode of illumination was that its production was a matter 
of great uncertainty. At last it was found that great precision was required 
in the position of the lamp-flame, which needed as accurate centreing as the 
test of the apparatus. This was at last effected by means of a lamp with 
vertical and horizontal screw adjustments, which enabled the narrow edge of 
the flat flame employed to be accurately brought into position. The lamp is 
figured in the “ Monthly Microscopical Journal ” for April. 
The following process is recommended by Mr. C. J. Muller for cleaning 
Foraminiferae from chalk. Having obtained a quantity of the shells by the 
usual process of elutriation, mix it with four or five times its bulk of silver 
sand which has previously been well washed, and put the mixture in a long 
2 or 3 ounce phial with a sufficiency of water. Shake up the whole (not 
violently) for ten or fifteen minutes, and then pour off the turbid water. 
Renew this operation as many times as you like. The Foraminiferae will 
always settle down last, and form a distindt stratum upon the surface of the 
deposited sand. The sand when shaken up with the shells will adt as a gentle 
rasp, and remove from their surface most of the hard granular particles which 
injure their appearance. When the cleansing operation is completed the water 
will rapidly clear upon the mixture being set aside for three or four minutes. 
There is no difficulty in separating the shells from the sand. Let the whole 
quietly settle down ; pour off the clear water, and allow the whole to rest for 
a few minutes. Now add a fresh supply of water rather forcibly, when the 
shells will immediately rise, leaving the sand below. The water with the 
shells must now be poured off, before they have time to settle down, into 
another vessel, where they may subside. The deposit may then be dried and 
mounted as required. 
A series of very successful micro-photographs have lately been presented to 
the Royal Microscopical Society : they are the work of Edward H. Gayer, 
Professor of Surgery in the Medical College, Calcutta. The camera and other 
apparatus are arranged on a strong table, 2 feet wide and 12 feet or more long, 
the chief peculiarity being the facilities afforded for manipulating the mirror, 
microscope, and illuminating apparatus — a point upon which great stress is 
laid by Mr. Gayer. To effedt this the operator stands near the mirror, which 
receives the diredt rays of the sun through an aperture in a shutter, a cell con- 
taining a solution of alum or ammonio-sulphate of copper being used to inter- 
cept the heat-rays. This mirror is best made of silvered glass, with the silvered 
side upwards ; the pencil next passes through a large condenser, consisting of 
a photographic landscape lens of 10 to 12 inches focus ; the usual achromatic 
condenser of the microscope is used if needed. The body of the microscope 
is connedted by a cone with the camera, which is most conveniently made 
entirely open : when in use it is covered with a black cloth, which is supported 
by the ends and diaphragms. The focussing screen consists of a sheet of 
albumenised paper pasted over a glass plate : two diagonal cross-lines should 
be drawn to assist in centreing, and a word in small type pasted in the middle. 
The focussing is effedted by means of a telescope made of the objedt lens of a 
large opera-glass and one of the eye-pieces of the microscope, connedted by 
means of a suitable length of tubing. This contrivance enables the operator 
