ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
509 
carries eye-pieces of the Continental size ; it gives tlio optical tube- 
length of 160 mm., for which the object-glasses aro adjustod, and is 
extended by means of a draw-tube to 200 mm. The fine-adjustment is 
sensitive and direct in action, and being independent of set-screws is 
not subject to derangement ; its fitting is by a new contrivance com- 
pletely covered at all points, and is thus preserved from injury by 
dust. 
The instrument can be obtained in a rigid form, and with sliding 
tube instead of coarse-adjustment. A petrological stand is also made 
similar in size and form to the foregoing. It has a revolving circular 
stage divided to 360°. The analyser, which can be drawn out when not 
needed, is fitted into the lower end of the body-tube, where also a slot 
is cut at the angle of 45° for the insertion of the quartz wedge. The 
polarizer is pivoted to swing out of the field, it has a circle divided into 
eight and clicked at 0° and 180° to indicate when the nicols are crossed. 
The eye-piece is furnished with crossed webs. 
Fig. 41. 
Messrs. J. Swift’s new Mechanical Stage (fig. 41). — This stage 
was described by Dr. W. H. Dallinger at the meeting of the Society for 
June last (see p. 537). 
(2j Eye-pieces and Objectives. 
New Objective Setting.* — Dr. R. Steinheil has devised a new method 
of mounting the lenses of large objectives in their setting, by which the 
unequal expansion of the glass of the lenses and the brass or steel of 
the setting is compensated. The mode of compensation hitherto used 
in large objectives has been by means of a spring on one side of the 
setting, but this has the effect of destroying the centering of the objective 
owing to the unequal expansion of the crown and flint glass of the lenses. 
The author obviates this difficulty by placing between the glass and the 
setting small rods like the spokes of a wheel. In order that these rods 
may have the effect of equalizing the different expansions, the material 
of which they consist and their length must be settled by calculation 
* Zeitschr. f. Instrumentenk., xiv. (1894) pp. 170-3 (1 fig.). 
