Tue MIcROscoPE. 19 
ing criminal prosecution, I determine the character of the sub- 
stance from the crystals found. Should they be lard, no 
further investigation is necessary. 
Crystals of butter are never seen until the substance is 
boiled. 
Prof. Weber's experiments have no relation to my investi- 
gations, neither will they effect criminal proceedings against 
offenders of the butter-laws of the District of Columbia. 
ASTIGMATISM AND THE MICROSCOPE. 
W. J. MARTIN, DAVIDSON COLLEGE, N. €. 
HAVE read with some interest the articles of Mr. Gundlach 
on “Astigmatism and Its Relation to the Use of Optical In- 
struments,” and Dr. Stockwell’s criticism of Mr. Gundlach’s pro- 
posed remedy. 
Dr. Stockwell suggests the use of suitable spectacles by as- 
tigmatic observers, instead of specially corrected eye-pieces as 
proposed by Mr. Gundlach; and the latter gives several reasons 
for the statement that “spectacles should never be used with 
any optical instrument, however great or of whatever nature 
the optical defect of the eye.” I have nothing to contribute to 
this discussion except my own experience; but as this is ex- 
actly in point I send it to you. My eyes are astigmatic, and I 
use sphero-cylindrical glasses to correct the defect. Formerly 
I was in the habit of laying aside the spectacles when I used 
the microscope; but latterly, to avoid the inconvenience of 
putting them on and off, I grew into the habit of using them 
while observing. And I fancied that I gained somewhat in 
clearness of definition. I had never set about testing this im- 
pression till I read Mr. Gundlach’s statement in the March 
number. I then made a number of experiments such as this: 
with a combination of eye-piece and objective which would 
just fairly show me the lines on a given shell of P. angulatum 
when I used the spectacles, I could not see the lines at all with- 
out the spectacles. This was true both by daylight, good and 
poor, and by lamplight. And in every case where test objects 
could be seen both with and without the spectacles, the defini- 
tion was better when they were used. The advantage in my 
case is not very great, but it is unmistakable. Whether a 
