Notes . 
248 
finishing touch is completed, if the face of the lens is seen to 
run out of truth (ascertained by the usual candle test), the soft 
metal will yield to a moderate degree of pressure applied to the 
proper side ; the burnishing may then be completed without fear 
of the lens wabbling, and, finally, the edges neatly finished with 
the turning-tool. The soft tin plies so well round the glass that 
no leakage occurs with any kind of oil or spirit ; and lenses thus 
mounted may be pushed out from the back of the cell for altera- 
tion or repair, without risk of fradture, as the tin is easily raised 
up without the application of a dangerous degree of force. The 
volatile oils and spirits used for immersion lenses act energetic- 
ally in softening and dissolving either Canada balsam or shellac, 
and it will not answer to employ these substances for rendering 
them oil-tight. For the purpose of making a leaky joint tight 
Mr. Wenham has found ordinary sulphur to answer perfectly, as 
it is not acted upon by any cold immersion fluids that can be 
used ; and as its melting-point is about 220° F., the heat required 
for its employment will not injure the coat of lacquer on brass 
work. In order to cement a front lens oil-tight in its cell it is 
sufficient to place this, with the lens fitted in position, on a hot 
plate, and drop a fragment of sulphur on the lens, raise the 
heat till the sulphur melts and flows round the edge. By capil- 
lary attraction it runs into the joint. Although melted sulphur 
is very fluid, yet it has a singular disinclination to attach itself 
or spread on a polished surface of glass ; and this property pre- 
vents it creeping over the back of the lens as balsam or shellac 
would do, and when cold the button of sulphur may easily be 
picked off with a needle-point, leaving the surface of the glass 
clean. 
Some years ago a standard screw for the fitting of objectives 
was determined on by the Royal Microscopical Society, and tools 
were issued, the result being the universal adoption of the 
Society’s gauge. Latterly the stock has become exhausted ; the 
Council have, however, completed arrangements for a further 
. supply : sets, consisting of a gauge and pair of screw tools, can 
now be obtained on application to the Assistant-Secretary. 
A writer to “ Science Gossip ” recommends the following con- 
trivance for conveying moist specimens by post : — Thin gutta- 
percha, such as is used by surgeons, is cut to the required size. 
The joint is made by dipping a camel-hair brush in chloroform, 
drawing it along the edge, and then placing the part to be joined 
to it before the chloroform has evaporated. If the tubes are only 
three parts full, it will allow of a little pressure should it occur in 
transit. The cover can be made by rolling brown paper over a 
ruler or other suitable form, fastening with paste, as firework 
cases are made, allowing to dry, then cut to lengths required. 
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