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McARTHUR PORTABLE COMPOUND MICROSCOPE

C. 1970

SIGNED ON THE RIGHT UPPER FRONT: 'McArthur Microscope, The Open University Model, Patent Applied for'

SIGNED ON BACK ON RED LABEL: 'Supplied by C.E. Offord Microscopes, Hurst Green, Sussex'

SERIAL NUMBER: 01056

MODEL: OPEN UNIVERSITY MCARTHUR PORTABLE MICROSCOPE (2 objective version)

Please Click on any Image for a Larger Version

Please Click on any Image for a Larger Version

DESCRIPTION:

This instrument, made almost entirely of plastics, measures 5 inches X 3 inches X 1 inch. It has glass optics. Other than the inverted design, it has several features which differ from the other McArthur microscopes. The eyepiece is fixed and not removable, as are the objectives. There is no extension of the stage to either side as in the usual contemporary McArthur microscopes; indeed a slide could be viewed with its long axis parallel to the microscope's long axis. There are plastic pieces permanently affixed to the condenser arm, curving downward to act like stage clips. The condenser is also permanently in place. It usually came with two objectives, but there was also a three-objective model. There was also a polarized light version.

The patented combined illuminating apparatus and switch was a new design as shown in the patent drawings. The three position control is marked in positions from back to front, labelled 'direct view', 'external lighting' , and 'electric lighting'. Direct view, meant that one could look through the condenser as one centered the specimen. A reflector moved into position for exterior lighting, and pushing the switch, which contained the electric bulb, all the way forward placed the light above the condenser and simultaneously completed the electric circuit as the contacts on the bulb receptacle came into contact with the contacts projecting down from the switch cover. For some reason, the battery compartment is smaller in diameter than standard AAA batteries and a bit larger than AAAA batteries-special batteries were apparently available for it when produced. To use it today, requires an external wired powered source, a modification to the battery compartment, dismantling modern 9-volt batteries to obtain the cells within, or putting in AAAA batteries with some space filler, perhaps the easiest.

The microscope has slots, one under the eyepiece, one under the condenser, and one under the objectives. The purported use of these was for examining microfilm. The obvious other use could be for analyzer and polarizer. The microscope is contructed in layers held together by small nuts and bolts; the nuts are slotted in one of my examples requiring special tools to disassemble the microscope. The other example has easier to access screws. Focusing, as in the metal versions, is achieved by bending the slider holding the objectives upward; unlike the metal versions though this is by a direct-acting plastic screw from the bottom. The instrument is labelled with instructions: 'SLAKEN focus screw after use,' a precaution to prevent the plastic from losing its elasticity. When supplied outside the University, it was sold in a box, with an instruction pamphlet, and had serial numbers. The actual OU models apparently lacked serial numbers. In addition, there are slight variations in construction, including the type of fasteners used to assemble the scope, etc. See the image at the left for a comparison of two variations.

HISTORY:

About 1971 the Open University in the U.K. needed many thousands of microscopes within a short period of time. They needed to be inexpensive to make, not prone to breakage, and easy to use. The two things most likely to go wrong with a microscope in the rough hands of young students, are failure or breakage of the rack and pinion of the coarse focus, or, in the course of focusing, racking an objective through a slide, ruining both the slide and the objective. Mirrors are also prone to loss or damage. All of this was eliminated with McArthur's new design. This design, patented by Dr McArthur, (application No. 19259/70, filed in April of 1970), provided all this and more. The patent specifically addresses McArthur's newly designed illumination system as described above, and also shown diagramatically in the patent drawings shown to the left. The drawings show how the lamp and reflector can be moved into any of the three positions, the first allowing visualization of the location of the specimen throught the condenser, the second allowing outside illumination to be reflected on the specimen, and the third which both moves the electric bulb into place and simultaneously completes the electrical circuit. There were three variations originally available, the usual form is seen above. Another with three objectives was also available as was a polarized light version with a rotating stage attachement. The two-objective standard version, sold for £15.50. A three-objective version (with a 40x added) sold for £29. The polarizing version cost £38.80. According to a 1972 Design Magazine publication quoting Dr McArthur it was made by Scientific Optics Ltd of Hastings, England. This is confirmed on the box of several examples.