Microscopical Society of Victoria. 
103 
the intervening spaces, to thoroughly secure the cover, a deposit 
of dew has almost invariably made its appearance in a short time, 
due, as I afterwards found, to the cement itself. 
Since reading the article above quoted, I have adopted the 
following very simple plan of mounting objects to allow of the 
circulation of air through the cell: Take an ebonite cell, and if 
necessary trim the edge neatly with a file, then with a file or 
knife cut two opposite broad shallow notches on that side of the 
cell which is to be underneath ; then cement the cell to tho slide, 
taking care not to allow the cement to fill the notches, which, 
being shallow, are quite unnoticed unless looked for. The object 
may be placed in the cell, and the cover cemented on at leisure. 
If a bright edge be required to the cell, it is only necessary to 
paint it with a thin solution of balsam or dammar, and no varnish 
ring on the cell is requisite (unless some other color than black be 
desired), as the ebonite cell supplies in itself a sufficiently neat 
finish. 
Those who are in the habit of using the excellent slides made by 
gluing perforated wooden slips to strips of card, can easily provide 
for the circulation of air by making one or two small slits in the 
card bottom of the cell. 
To obtain the freest circulation of air through the cells it will 
be advisable to leave the slides in an open rack box till the cement 
has hardened, rather than to close them up at once in a cabinet. 
(2.) Vacuum-bubbles in Canada Balsam .—One of the first 
difficulties which a novice in mounting meets with arises from 
the formation of air-bubbles in Canada balsam, but experience 
soon shows him that if the balsam be used in not too thick a state, 
any bubbles that may form in it will, unless they are excessively 
large, gradually disappear in the course of a few days at most, and 
henceforth air-bubbles in the balsam cease to be a source of trouble* 
It is otherwise, however, with vacuum-bubbles, which are apt to 
appear in any closed cavities of an object at the moment of 
applying the balsam, even though every cell may have previously 
been perfectly filled with turpentine or carbolic acid. The cause 
appears to lie in the different densities of the fluid and the balsam, 
the former finding its way out of the cell to mix with the balsam, 
while tho latter, owing to its greater density, is unable to enter 
the cell and supply its place. A vacuum is therefore left, which 
