1881.] Microscopy. 419 
were separated from the rest of the coarser, rounded and lighter 
fragments of vein-stuff and country rock. The pyritic matter is 
then tested for gold, silver and tellurium, and also a microscopic 
examination of it is made under water. The fragments of coun- 
try rock and vein-stuff are then washed again, using a brush to 
rid them of any clay that might still adhere to them. After dry- 
ing, they are put into a separator having sieves with 30, 50 and 100 
holes to the linear inch—a uniform size enabling me to examine 
them better with the microscope. The fragments that pass 
through the sieve having 100 holes, I place in a small cell, fastened 
on the glass slide, and filled with water, which I cover with thin 
glass—the shape of the fragments are seen much better in this 
way, since by slightly moving the thin glass cover, they can be 
made to turn and exhibit their forms in different directions. 
ARRANGING SMALL OBjects ON SLipEs.—Mr. Julien Deby pro- 
poses to facilitate the arrangement of diatoms, foraminifera and 
other small objects on slides for mounting, by drawing on the 
plain mirror of the microscope regular lines in crosses, circles, or 
any desired patterns. The achromatic condenser being so focussed 
that the image of these lines shall be in focus of the objective at 
the same time with the object slide, there is no difficulty in simi- 
ey arranging the objects by hand or by means of a mechanical 
nger. 
Tue Harrnack Microscorgs.—It is now eleven years since 
Hartnack was—in common with other Prussians during the Fran- 
co-Prussian war—compelled to leave France. He immediately 
Settled in Potsdam, and there established an optical factory for 
microscopical work. M. Prazmowski, who had. been for several 
years working with Hartnack, was admitted into partnership, and 
took entire charge of the house in Paris. The exhibit of micro- 
Scopes, &c., at the Paris Exhibition of 1878, was by the firm Hart- 
nack & Prazmowski. Since that date the partnership has been 
dissolved ; the Potsdam house remaining exclusively Hartnack’s, 
and the Paris house Prazmowski’s. It is well known in Paris that 
to M. Prazmwoski’s mathematical attainments have been due the 
yeats or — M.S. in Eng. Mechanic and World @ 
tence 
New Sea-sip— Lasoratory.—Professor A. Hyatt, the curator 
me History, will be under the immediate care of Mr. B. Vi 
ck, assistant in the Museum and Laboratory of the Boston So 
ciety of Natural History. Students are advised to bring their own 
