32 Tue Microscope. 
into use and when not needed it may be easily removed, leaving 
the perfect eye-piece ready for use under the normal eye. 
Many, in fact most, astigmatic persons have a different de- 
gree of defect in each eye, and therefore a better plan would 
be to have suitable cylindrical lenses put into spectacle frames 
and they worn only while using the microscope. These can be 
placed near the eyes, the axis of each is firmly held in its proper 
relation to the effective medium and each eye has before it the 
exact correction of that eye’s asymmetry. To be sure this re- 
quires the aid of a skilled specialist; but once done there is no 
further trouble or anxiety. No feeling around with test-lines 
in order to be sure that the glasses are in the best position for 
work. 
Secondary distortion because of being a little distance from 
the eye-lens of the instrument is not troublesome, nor worth 
considering as against convenience, comfort and the ability to 
instantly change eyes when working—an important desidera- 
tum. 
The article, of which this may very properly be considered 
a feeble criticism, should arouse astigmatic microscopists to the 
importance of correcting their defective eye-sight, which, hay- 
ing done, will enable them to use their eyes with greater comfort 
than formerly, observe more correctly and perhaps find less fault 
with the performances of their objectives. 
THE RELATIVE MERITS OF FILAR AND ORDINARY 
GLASS EYE-PIECE MICROMETERS. 
BY M. D. EWELL, M. D., LL. D. 
Es the June number of the American Journal of Microscopy 
for the present year is a short article by Mr. H. L. Tolman, 
giving the results of the measurements by himself and the 
writer of 75 human red blood-corpuscles, 50 of which were 
measured by Mr. Tolman with a Spencer #, and an ordinary eye- 
piece micrometer, giving amean diameter of ;7;5 inch and 25 by 
the writer with a Spencer ;;, Bausch & Lomb amplifier, and 
filar micrometer manufactured by Mr. Bulloch, of Chicago, 
giving a mean of ;;,;; inch, from which Mr. Tolman drew the 
conclusion “thatthe cob-web micrometer does not offer sufficient 
