114 MEMORANDA. 
trough, so that the tail les im the cell © Fr G H, a small 
quantity of water is placed in the trough, and the fish kept 
in its place by one or two elastic bands or strips of thin sheet 
lead passing round the glass, and over the body of the fish. 
The advantages of this arrangement are— 
Ist. The fish cannot throw up his tail and splash the 
object-glass with water. 
2d. In consequence of the tail being kept flat in the 
cell the view is very good, and there is little risk of the object 
getting out of focus. 
3d. If the tail is not pushed too far into the cell the 
vessels at its root are not compressed, and the circulation 
goes on very freely. 
4th. The fish may be kept on the stage of the microscope 
for two or three hours without injury. 
Mr. Macaulay, a philosophical instrument-maker in Leeds, 
has suggested, as an improvement, that the three sides E B, 
BD, and pH, should be made of a single slip of plate glass 
bent to the shape required.—W. R. Miner, Wakefield. 
On a mode of Illumination for High Powers.— Making pretty 
frequent use of a one-quarter-inch objective by artificial 
illumination, I found it a point of some importance, to 
be able to get rid of the glaring fog, which often occurs, 
in a ready and expeditious manner. The ground-glass 
screen for use with the lower powers seemed to me to 
be the readiest cure for the evil complained of; but, as 
usually mounted beneath the stage of the microscope, it 
is inapplicable in the case of the higher powers, from its dimi- 
nishing the light too much; and the only plan seemed to be to 
place it immediately under the glass slip carrying the object. 
I accordingly ground, with fine emery and water, the surface 
of a polished slip of glass 8x1 inches, and placed it on the 
stage of the imstrument, throwing a moderately strong 
light up from the mirror in the usual way. I then tested 
the arrangement with several mounted slides of objects cal- 
culated to try its efficiency, and I am glad to say that it 
succeeded perfectly. Besides the freedom from glare, and 
the rendering of the light very pleasant to work by, the 
thorough dispersion of the rays imparts a very valuable pro- 
perty to this method of illumination, which is at once 
apparent in the manner in which it shows objects of high 
refractive power. The sheathing scales on hair and wool, for 
instance, are brought out remarkably well; the discoid 
Diatoms in guano, sponge-spiculz, starch-granules, spiral and 
scalariform tissue, the cell-contents-in Algz, are also shown 
