DESCRIPTION OP PlJVTE 6. 
FIG. i. In its present form the universal stage comprises, when attached to the micro- 
scope stage, five graduated circles: H t , the horizontal circle of the microscope stage; H t , 
the large horizontal circle of the universal stage, with Hi, the inner and thin section- 
hearing circle; I 1 ",, the large vertical circle, and V t . an inner circle consisting of two seg- 
ments, V ta and I'jft, which serve to measure the angle of rotation of the inner disk 77, about 
the horizontal axis. Two glass hemispheres (Ai being the upper) are usually employed 
with the stage to increase the angle of view of the microscopic field. 
FIG. 2. Universal stage fitted with upper lens of condenser system, thus producing a 
universal condenser with which optic axial angles can be measured directly and plates 
can be tilted definite angles in any azimuth. Especially serviceable with high-power 
objectives in convergent polarized light. 
FIG. 3. New ocular for use with the petrographic microscope. Consists of holder B, 
which fits into the draw tube of the microscope as an ocular and carries the Ram^U-n 
eyepiece A and an opening at B into which different wedges and plates can be inserted 
and different optical properties thereby measured. The three plates shown are (a) 
graduated combination wedge used in the measurement of birefringence, the graduations 
cm the wedge giving directly the path-differences in nn for sodium light; (b) bi-quart/ 
wedge plate for measuring extinction angles; (c) o.i mm. coordinate micrometer scale 
for measuring optic axial angles on sections in which at least one optic axis appears in 
I lie field of view. 
