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SUMMARY OF CURRENT RESEARCHES RELATING TO 
analyser, and the field of view is correspondingly limited by the dia- 
phragm c. 
For exact microscopic measurements in the field of view such as 
cannot be effected by the ordinary glass micrometer, a screw eye-piece 
micrometer is used. It is particularly adapted for the measurement of 
the apparent separation of the optic axes. It consists of a long four- 
sided box, in which, by means of a micrometer- screw and counter spring, 
moves a slide A, in the central opening of which is a diaphragm, across 
which at an angle of 30° two spider webs are stretched. 
Ftg. 39. Fig. 40. 
The eye-piece goniometer, seen in fig. 39, serves for the measurement 
of plane angles. The tube a, which fits into the body-tube of the 
Microscope, carries in its upper part the diaphragm e, which is held by 
four screws i. Over this is drawn a thread passing exactly through 
the axis. With the circle d divided in half-degrees is connected the 
Eamsden eye-piece with the dia- 
Fig. 41. phragm /. The latter is approached 
as near as possible to the diaphragm e, 
g and also carries a thread centered ex- 
actly in the axis. 
In fig. 40 is shown the measuring- 
apparatus of Becke for use when the 
axial images are observed by Klein’s 
method of placing a lens above the 
Ozapski eye-piece. In a tube fitted 
over the Czapski eye-piece is the ap- 
lanatic lens O. Under this is the 
micrometer-scale M, which can be ad-* 
justed in the direction of the axis 
by the two milled heads & and Jc'. For the observation and measure- 
ment of the axial image, the Klein’s lens is placed above the Eamsden 
eye-piece, adjustment is made with the objective 0, and the micrometer M 
is raised or lowered so as to coincide in position with the image formed 
by the Eamsden eye-piece. 
