ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
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the polarizer for axial illumination ; the substage focusing adjustment is 
by a spiral screw actuated by the small milled head, which in the figure 
is shown immediately over the mirror. 
The polarizing jmsm is in a revolving fitting which is divided on 
its circumference ; it has a catch to hold prism at points of extinction. 
The analyser is mounted in a sliding box, and is fitted in the tube of 
the instrument ; beneath the analyser is a Klein’s quartz plate, also 
mounted in a sliding fitting, and either can be immediately removed 
from the axis of the instrument. 
The double mirror is arranged on an arm to swing in and out. 
New Microscope for Observations at High Temperatures.* — 
Mr. Yon Wyronboff has had constructed by Nachet a polarization 
Microscope for the examination of objects at temperatures up to 600°. 
It is claimed to be simpler and more serviceable for the object in view 
than the Lehmann instrument, chiefly owing to the long focus given to 
the objective. The object lies on a perforated ring-shaped sheet of 
copper which is heated by two Bunsen burners and is attached to a 
special insulating support to prevent any heat being conducted to the 
body of the Microscope. As the object therefore cannot be moved, the 
whole Microscope is made to revolve in a horizontal semicircle and can 
be also moved horizontally by two guides. 
From the description of this wonderful instrument we learn that 
the “ motions provide for the measurement of inclinations due to extinc- 
tion,” and that “ the instrument does not exactly measure temperatures, 
but some thermometric substance.” 
(3) Illuminating: and other Apparatus. 
Substage Apochromatic Condenser with Collar Correction. — At 
the Society’s meeting on March 20th last, Mr. E. M. Nelson read the 
following note : — “ The apparatus before you this evening can hardly be 
called novel, for it was suggested by me some ten years ago ; I believe, 
however, that this is the first actually constructed. The reason why 
my first suggestion was not carried out was owing to its being stated on 
all sides that the game was not worth the candle ; but practical results 
now obtained disprove this statement. 
The mechanical arrangement is very simple : the correction collar 
is similar to that of an ordinary objective, it has a steeper spiral slot, 
and only half a revolution of movement ; a long arm is fixed to the 
collar so that it may conveniently be reached by the finger (fig. 32) , 
Mr. Powell has constructed it so that it will turn easily and smoothly at 
the slightest touch. This is an important point ; for if the movement 
were as stiff as the collars on some objectives it would be impossible to 
move the collar without throwing the condenser out of centre. It is 
needless to state that the collar moves only the back lens of the com- 
bination, leaving the mount rigid. 
The object of the correctional movement is primarily to increase 
the maximum aplanatic aperture of the condenser ; this is effected by 
separating the lenses. If the back of a wide-angled objective be 
examined, when an object is illuminated by the full aperture of the 
* Amer. Micr. Journ., xv. r (1894) pp. 352-3. 
