148 THE MICROSCOPE. Nov 
dicular to the direction of the motion. Hence a small 
blade has been provided which can be secured in the 
same socket as the larger one. Seek, fig. 2. As those 
two screws which are parallel to the edge of the blade 
must be fixed, while the opposite one is the micrometer 
screw, the position of the screws must now be arranged 
as in fig. 2. 
With this instrument celloidine sections can be cut as 
thin as ten micromillimeters and paraffin sections as thin 
as three micromillimeters. In fact the thinness is limited 
only by factors which apply to any microtome, namely, 
the sharpness of the knife and the quality of the speci- 
men. 
The practical advantages of the instrument over other 
microtomes result from its mathematical construction. 
Theoretically the entire motion is determined by three 
points, the smallest number which can, geometrically, 
determine a plane. Furthermore, the knife moves one- 
fifth as much as the micrometer-screw; hence any error 
in the thread of the screw will be divided by five. While 
these facts may be of little value in the actual cutting of 
a section, they afford usa great practical advantage, 
namely, that the instrument depends for its accurate 
working more upon its inherent mathematical construc- 
tion than upon the technical skill and workmanship ex- 
pended in its manufacture. Hence it can be made much 
cheaper than the usual forms of microtome. In fact, - 
the instrument, including both paraffin and celloidine 
blades, can be obtained for ten dollars of Messrs Treman 
& Co., of New York City, who have skillfully carried out 
the ideas on this instrument. 
New Factory.—As soon as our new building is com- 
pleted we will be pleased to send you a cut of it together 
with a description.—Gundlach Optical Co., Rochester, N. 
Yo, HH. . DPurner, .Manasex: 
