Combined Binocular and Monocular Microscope. 
Due to the comfort and freedom from eyestrain afforded by the use of both eyes, the binocular 
microscope has, of late years, increased in popularity. The microscope here described is specially 
designed so that binocular and monocular observation can be alternatively employed by a simple 
interchange of two bodies. In the binocular body the greatest care has been taken to ensure that 
the optical performance is of the highest order with both high and low powers, and features are 
embodied not hitherto found in binocular instruments. The tubes of the binocular are inclined 
towards each other, at the natural convergence angle of the eyes when working under indoor 
conditions. This method has always been adopted by all makers, in the low power binocular 
and the Greenough binocular and the advantage applies to high power binoculars, with equal 
force, all eyestrain involved in the use of parallel tubes being avoided. When objects at a 
distance are viewed the two eyes naturally look out in a parallel direction, but indoors 
or even when inclining the head downwards, they automatically converge to a near object. For 
this reason a binocular microscope constructed with parallel tubes is fatiguing to use. A con- 
venient adjustment actuated by a screw motion and a milled head is provided for setting the 
interocular distance. One tube has an adjustment to compensate for any difference in focus 
between the two eyes, and a locking device is fitted to clamp it in the correct position. The 
monocular tube is fitted with an extending drawtube and is required mainly for photomicrography, 
drawing and measurement. 
The binocular and monocular bodies slide interchangeably on a dovetailed fitting and can 
be clamped in any position. In addition to providing a quick and easy means of interchange, 
this provides a method of varying the tube length, compensating for different thicknesses of 
cover glass and mounting material. Such a feature is not found in most binocular microscopes. 
The tube length is 160 m/m. when a revolving nosepiece is in use, without the intervention of any 
optical correctors. By the means above mentioned, it can be extended for 35 m/m. 
The microscope is supplied in a number of different models. One model has a large square 
stage to which a detachable mechanical stage can be applied. This stage has a travel of 24 in. 
by 1 in., so that practically the whole of a 3 in. by I in. slide can be examined. Others have built- 
in mechanical stages, either with a travel of 4 in. by }in., 1} in. by 1 in., or 3in. by 14 in. These 
are square and of sufficient size for holding large specimens which can be mechanically moved 
and can be cleared of all obstructions so that large dishes are accommodated. In the two with 
the smaller travel the top plate is moved by the mechanical motions. In the other, the lower 
plate travels, giving the vertical motion and the slide moves over the top stage plate for the 
horizontal motion enabling a travel of 3 in. to be obtained. This stage is illustrated on page 
84 (No. 3515). A further model has a rotating circular stage with centring adjustments, either 
plain or with mechanical motions. 
Four forms of substage are provided. They are all focussed by rack and pinion motion. 
The simplest form has no centring adjustment and is suitable for use with the non-achromatic 
condenser. For use with the achromatic condenser a centring substage is required and this is 
made in two forms, one fixed in the optic axis and the other capable of being swung aside when 
desired. In the other form the substage apparatus is changed by means of dovetailed (Akehurst) 
slides. In this the pieces of apparatus where necessary have centring adjustments upon the 
slides so that they may be individually centred. The great feature of this substage is the rapidity 
with which the condensers can be interchanged, without disturbance of the adjustments. 
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