struction of this can be seen by the illustration (page 24). It is fixed to the stage by means of screws 
which engage in the stage clip holes. It can therefore be used to position slides upon the stage 
in conjunction with verniers which can be fitted if required. The Topley top stage affords 
a very easy and certain method of holding the slip and can be readily removed when a clear 
stage is desired for the accommodation of petri dishes or troughs. The whole mechanical stage 
is of a particularly robust construction and the mechanical motions give smooth and easy move- 
ments free from backlash. The Pathological microscopes (Nos. 31 and 3741) are made with 
the front part of the stage cut away as illustrated below. By this means the substage 
apparatus can be withdrawn from the instrument without any movement of the substage, so 
that a condenser and a dark ground illuminator can be interchanged without any movement of 
the rack and pinion and with practically no disturbance of the adjustments of the instrument. 
Body in Nos. 3740 and 3741 is of a large 
size, 2in. in diameter, and in Nos. 31 and 32 
of the smaller diameter as illustrated on page 26, 
Each form has an adjustable drawtube which is 
divided in millimetres, enabling any tube length 
from 140 m/m to 200 m/m to be used. The 
lower end of the drawtube has a standard R.M.S. 
thread to carry an erecting lens or a very low 
power object glass. 
Limb is of solid construction and of a 
convenient shape for lifting the instrument. The 
shape of the limb in the model with the smaller 
body tube is as illustrated on page 26. The shape is 
slightly altered in the model with the large sized 
body tube. 
Coarse adjustment is by means of spiral 
rack and pinion cut on specially made machines 
to ensure an accurate and smooth movement. The 
milled heads are 1} in. diameter. 
Fine adjustment is on a patented design and is operated by two milled drums, one on 
each side of the limb. The adjustment works with levers and point contact, and only by 
this means can the necessary delicacy be obtained. The friction is reduced to a minimum, and 
all drag and heavy movement and backlash is thus obviated. 
Substage is one of the principal new features of this microscope. As_ referred to 
before, cylindrical systems for changing substage apparatus are not entirely satisfactory, 
especially when frequent and rapid changes may be necessary. The substage of the Patho- 
logical microscope employs dovetailed slides, the principle of which can be seen from the illustration 
on page 26. Each piece of apparatus is fitted to a slide with a projection for holding, and is 
slid into the dovetail in the substage itself and clamped in position by a screw with milled head. 
By this system the changing is easy and certain as the slide is forced up against one side of 
the dovetail and must therefore take up its correct position. The substage is focussed by rack 
and pinion. 
Mirror is double, plane and concave, of 2 in. diameter. 
The instrument is contained in a mahogany cabinet with carrying handle. 
High power binocular eyepieces as described on page 76 and 77 can be fitted to all models 
and the angular eyepiece attachment as described on page 77 will be found a most useful addition 
where the microscope is used in vertical position. 
75) 
