198 
noo:es and memoranda. 
carries also a second slide, parallel with, and at the back of the other, 
by means of which a slow adjustment is obtained by the action of a 
stout steel lever passing through a channel in the limb ; the lever is 
acted upon by the ordinary micrometer screw in conjunction with a stiff 
steel spring. This arrangement permits of the milled head of the 
fine adjustment being placed in a most accessible position, on a step 
above the trunnions supporting the limb and body of the microscope, 
almost similar to the fine adjustment in the old Eoss model. This 
simple fine adjustment, when in use, leaves the body of the instru- 
ment quite untouched, and therefore not liable to swerve ; an evil of 
common occurrence in cases where the fine adjustment is attached to 
the body itself. The magnification of objects is not altered by a 
difierence in the length of body, as is more or less the case when the 
fine adjustment is obtained by means of a cylinder sliding in the 
nozzle of the instrument, and the thickness of an uncovered object 
on the stage can be directly measured by means of a divided scale 
and vernier which can be attached to the limb at the edge of the fine 
focussing slide. 
The most important feature of the Zentmayer stand consists in 
an improved method by which the tail-piece or stem carrying the 
mirror, sub-stage, with all illuminating apparatus, can be turned aside 
or swung on a tubular pivot (placed at the back of the stage), the 
centre of which is in a line in the optic axis intersecting the plane of 
the object on the stage, and consequently also in the focus of the 
object-glass. 
The use of this swinging tail-piece arrangement enables condensing 
and other lenses for concentrating light to be used at any angle below 
or even above the stage if required, affording peculiar facilities for 
obtaining oblique illumination, and in the adaptation of appliances to 
be used for the purpose. For registering the angle at which an object 
is best observed there is a divided arc on the upper segment of the 
swinging stem. 
With the usual form of microscope stand, in which a fixed stem 
supports the sub-stage, oblique light has to be obtained either by 
the use of separate reflecting prisms or admitting light through 
peripheral stops from the margin only of high-angled condensers. 
These necessarily come very close to the slide, and there is a difficulty 
in regulating the obliquity of deficient marginal rays. In the 
Zentmayer stand, however, with the use of the swinging arrangement, 
condensers and illuminators of long focus can be used with great 
advantage, and abundance of light is obtained with low-power object- 
glasses such as the 1 inch and inch. 
In order to get the best results for oblique illumination a very 
thin stage was found to be requisite ; a simple mechanical stage, with 
concentric rotary movement, has therefore been designed specially 
for this instrument by Mr. Wenham, having only one movable plate 
in its construction, the rectangular directions of which are per- 
formed by two concentric milled heads, something similar to the 
well-known Turrel stage. This stage is supported by a conical stem, 
which passes through the tubular pivot of the swinging tail-piece 
