500 MICROSCOPY. 
pins in such manner that a dozen slides can lie, side by side, 
securely upon it. An equal number of thin brass wires spring 
from one side of the block, and are bent down so that they can be 
easily made to press upon the centres of the covers, to hold them 
in position while the balsam or other mounting material is hard- 
ening. Little cork disks are furnished to place upon the covers 
and beneath the springs. For some uses the corks would doubt- 
less be dispensed with, and when needed they would probably be 
more convenient if attached to the wires by passing the wires 
through them. An additional groove should be cut in the wood 
under one end of the glass slides to facilitate the removal of one 
slide without disturbing the others. 
Since Froxt Opsectives.—Mr. Wenham believes that the prin- | 
cipal use of the late discussion upon the working angular aperture : 
of immersion objectives viewing balsam-mounted objects, whieh a 
: 
= 
angle he still maintains is necessarily limited to 82°, although Mr. 
Tolles cannot see the difficulty of its exceeding that figure, Con- 
sists in the dissemination of the information that the best Amer 
ican objectives, both dry and immersion, are now made M 
single fronts. As the originator of this style of construction, 
though having at the time no knowledge of its importance "o 
expectation of the success it has since attained, he naturally feels 
an undisguised interest in its success. The triple-front objectives 
he considers already obsolete. f 
ocraTION.— During 
Microscopy AT THE AMERICAN MEDICAL Ass ee 
the Philadelphia meeting of this society, this summer, an m 
reception was given at the Academy of Natural Sciences, * io se 
music and sociability were supplemented by the entertainm’? 
afforded by microscopic specimens. One hundred microscope 
were used, and novel accessories exhibited. 
STRUCTURE or Draroms.— Prof. Adolf Weiss, of Lemberg: n a 
published some researches upon this well-studied but still ee ee 
subject. He regards the silicious envelope as capable of pe itrated 
light, and as consisting of a cellulose coat more or less inf pee” 
with silex. He does not consider the individuals oneal 
finds the valves composed of cells from .008 to 00025 ae 
diameter. These cells are furnished at their centres we 
which appear as striæ under low powers and as moniliform 
