Answers to Queries. I93 
I mount an object in the cell, let it dry thoroughly, place the slide 
on the turn-table, spin a ring of brown cement (Ward’s) upon the 
cell, allow to dry till it can be indented with the finger-nail without 
sticking. Warm a cover-glass and place it on the cell. Take a 
strong glass slip, make it hot in the centre with a spirit-lamp, and 
press it down on the top of the cover-glass. The warm melts the 
cement, and the cover is firmly fixed without evaporation inside 
the cell. Put the slide aside for a day or two to harden, and then 
add another layer or two of cement, and the dry mount is safe. 
If very shallow cells are used, brown-cement cells, which are 
allowed to get thoroughly dry and hard, are best. But before 
fastening on the cover glass, apply a second coat of the cement, 
and when this is just getting hard apply the heated slide as above. 
If opaque objects are wanted, the light may be turned off or a 
background used. Some very dark-coloured objects want a white 
ground ; then use white opal slips. A blue ground may be 
obtained by covering the bottom of the cell with fine powder-blue 
paper, and over both fasten a cover-glass. This forms a base 
upon which to place your true cell, and in which you wish to 
mount your object. It will be seen the coloured paper is out of 
focus when the object is looked at, yet the desired tint is obtained 
and is very cool and pleasant to the eye. Carbolized gum, to 
which add a few drops of glycerine, is good to hold objects in 
place, and is not brittle. Vi Aca; 
400.—Abbe Microscope Condenser.—In reply to B. R. F., 
I may say that I have used one of these for some time, though I 
believe mine is not of quite so high angle as Zeiss’ present form. 
The condenser is certainly a very convenient one and of easy use ; 
and replaces diaphragm and mirror and the ordinary illuminating 
arrangements. If the condenser gives too strong a light I remove 
it and use the stops instead of a diaphragm. I have had a 
ground glass diaphragm and one with slits at right angles fitted to 
mine, with advantage I think. Experimental stops of blackened 
cardboard are easily applied. 
As for dark ground illumination, with 600 diameters, this must 
depend very much upon the angular aperture of the lens. With a 
lens of 75° like Zeiss’, D (4”) it will give it with large angles; the 
oblique rays enter the objective. I have not a polariscope 
adapted to mine, so am unable to speak of its performance in that 
way. The chief objection to it is its weight and size. It is 
arranged so as to form substage arrangements for Zeiss’ larger 
stands ; Leith also, I believe, adapts the same kind of condenser 
on to his stands. Baker makes a simpler and lighter form of the 
above for some of his stands. This form gives central light and 
dark ground illumination ; oblique light must be obtained by special 
diaphragms and not by rack and pinion movement as in Zeiss’ 
