MICROSCOPY. 701 
passing over or through them and fastened to hooks or rings be- 
low. Such an apparatus, figured and described in “ Martin’s Man- 
ual of Microscopic Mounting,” p. 28, is inconvenient chiefly by 
reason of the difficulty of varying pressure by means of the elastic 
band. Mr, C. E. Hanaman suggests the employment, as a substi- 
tute for the rods, of glass tubes loaded with shot or mercury so as 
to give the required pressure by their weight. By merely un- 
Corking the tube and pouring a little mercury in or out all neces- 
sary changes of pressure may be secured, or the different tubes 
may be kept filled to different heights and the proper one chosen 
in each case. 
Tue xew Tyre Prate.—Méller has brought out another of his 
exquisite plates. This time he photographs, upon the centre of a 
glass cover, a square of about one-sixth of an inch composed of 
eighty circles surrounded by a black background with the name of 
a different diatom photographed under each circle. In the centre 
of each circle is mounted a diatom corresponding to the label be- 
low, two specimens being often introduced to show different views 
of the same form; of course all is arranged in inverted position 
on the slide, but under the microscope appears as described. The 
objects are mounted between two thin glasses which are set in a 
brass plate three and a quarter inches long and one and a quarter 
ide. 
Fixtna Dratoms.—Mr. J. K. Jackson, in a communication to 
“Science Gossip” laments that the best “diatomaniacs” hold so 
tightly the secret of their mounting, and details his own experi- 
ence for the assistance of others. The diatoms are carefully 
cleaned and a dip of the material containing them evaporated on 
a slip which is then placed under a 1} inch objective. The covers 
on which to mount have been previously glazed with gum by put- 
ting on the centre of each, carefully cleaned, a small drop of a 
Solution formed of an ounce of freshly distilled water and five or 
six drops of a freshly prepared solution of gum tragacanth or 
arabic; a number of covers being prepared at once on a wooden 
rack and dried over a hot plate in order to leave the least possible 
Opportunity for exposure to the ‘‘ vile inappreciable dust” of the 
room. With a hair from a cow’s neck, mounted in a wooden han- 
dle, a diatom is picked out from the dip, at the rate of from eight 
to ten per minute and disengaged from the hair by dabbing it on 
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