Compound achromatic microscope




United Kingdom


W.R. PRIOR & CO. / LONDON / 8473



Optical 1


Optical 2


Size of the box (h x b x d)

34.3 × 18.7 × 21.8 cm

Size of the microscope (h x b x d)

32.5 × 11.5 × 18.5 cm

Inventory number

SM 8


With the microscope goes its wooden box with a nickel-plated grip.
This is a fine example of a student microscope of the period. The microscope has a black enamelled cast horseshoe foot, on which the inclinable limb with the stage is mounted in a slit. The stage is made of ebonite, under the stage a two lens Abbe type condenser with its iris diaphragm. The block between the limb and the body carries the fine adjustment by worm screw and the coarse adjustment by rack and pinion. The microscope has a draw tube.
There is one Huygenian eyepiece, ‘4×10’, its focal length is 24.05 mm, and its magnification is 10.4× .
There are two objectives, mounted in a triple nosepiece changer, a ‘2/3’ and a ‘1/6’, both with nickel-plated front lens caps, RMS thread and engraved (by machine) ‘W.R. Prior & Co. London’. The objectives were investigated using the Bleeker microscope, with a 170 mm body tube, the ‘2/3’ with a 10× Huygenian eyepiece, the ‘1/6’ with a 5× Huygenian eyepiece..

Objective lens 2/3 1/6
Focal length (mm) 17.18 4.18
Magnification 96.43 216.48
Numerical aperture 0.26 0.9
SResolving power(µm) 1.3 < 0.8

The 2/3 objective was of good quality: good contrast, a trace of coma, a flat field, only a trace of distortion.
The 1/6 objective was less contrasty, it showed a trace of coma, a flat field and it was spherically well corrected. It resolves Pleurosigma angulatum into dots, Surirella gemma is just not resolved into lines.