NOTES AND CORRESPONDENCE. 
Ross's New Compressorium.—-Microscopists who have suf- 
fered the inconvenience inseparable from ordinary forms 
given to a compressorium, will thank us for calling their 
attention to an enterely new pattern devised by Mr. Ross. 
It consists of a stout plate of brass (A), about three inches 
long, having in its centre a 
piece of glass like the bot- 
tom of alive box. This piece 
of glass is set in a frame (B), 
which slides in and out, so 
that it can be removed for 
the convenience of preparing 
any object upon it, under 
water, if desirable. The up- 
per movable part D, attached 
to a screw motion at C, is 
admirable for simplicity and 
efficiency. At one end of 
the brass plate A, which 
forms the bed of the instru- 
ment, is an upright piece of 
brass (C), accurately grooved, 
so as to receive a vertical 
plate, to which a downward 
motion is given by a single 
fine screw, surrounded by a spiral spring, which elevates 
the plate, as soon as the screw. pressure is removed, by 
turning the milled head the reverse way. The vertical plate 
carries an arm precisely at right angles to its own plane, and 
terminating in a square frame (D) capable of receiving very 
thin or somewhat thicker glass, according to desire. This is 
the upper part of the compressorium, and the exact amount 
of pressure required is completely under command by the 
motion of a single screw. The arm has likewise a horizontal 
motion, so that the upper plate D can be turned completely 
