4 Tur Microscope. 
to find a suitable remedy, and, as such, I propose a most simple 
and effective one in the use of an eye-piece of an asymmetric 
form so as to just neutralize the asymmetry of the crystalline 
lens of the eye. This can best be done by making the outer 
surface cylindrical instead of spherical or plane. It may be 
made either concave or convex as the requirements of the case 
may demand. The eye-piece must be constructed with special 
regard to the purpose so as to place the asymmetric surface in 
such close proximity to the eye that no perceptible secondary 
distortion is produced by the oblique direction of the eye 
toward the edge of the field, and, at the same time, the prisma- 
tic colors dispersed in the direction of the astigmatic distortion 
must be neutralized. 
I intend to construct such eye-pieces, and expect to start 
with a one-inch. To enable the applicant, for this special pur- 
pose at least, to be his own examiner for astigmatism, I intend 
to furnish with the eye-piece three eye-glasses, alike in mount- 
ing but different in the degree of asymmetry, for selection. The 
difference being such as to practically approach both limits of 
conimon astigmatism, and the one of the three lenses nearest in 
asymmetry to that of his eye will correct his astigmatism to an 
undisturbing minimum. The observer will then have to test all 
the lenses, beginning with the weakest, on a suitable object, 
slowly revolving the eye-piece until its best position is found, 
Mark this position, and do the same thing with the other lenses. 
After this, compare the action of the lenses, each in its best 
position, to find the one best fitted for the eye. Of course the 
eye piece, or rather its asymmetric eye-lens, must then always 
be used in the same position to the astigmatic axis. To do this 
there will be no difficulty when using the microscope, but for 
the equatorially mounted telescope a special contrivance may 
be required, so that the position of the eye-piece may be easily 
controlled in the dark by the fingers and corrected after each 
change of the position of the body. - 
As soon as an “ exchange ” notice has served its purpose 
will the author of it please notify us, that we may make room 
for others now waiting. 
