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C. Baker's "Diagnostic" field microscope, London (1920's)

The "Diagnostic" portable microscope model, by C. Baker, London (c.a. 1925)

This is perhaps one of the most famous historical models of field (i.e. portable) research microscopes. Manufactured by C. Baker of London, one of the most prestigious scientific instruments makers of the time, the "Diagnostic" model has been conceived by sir Ronald Ross, when he was serving as a surgeon in the Indian Army Medical Service in the 1890's. Ronald Ross received the Nobel Prize in Medicine in 1902 for his discovery of the malaria parasite in the Culex mosquitos. His Nobel was contested by Giovanni Battista Grassi, who also discovered in the same years the malaria parasite in Anopheles, but was not included in the prize. Political reasons and the fierce anti-italian attitude of Robert Koch, one of the major sponsors of Ross, were probably behind such lack of recognition. During his service in India, Ross realized that in order to look for the parasite in the blood of the affected people in the most remote settings, he would have needed a robust, capable yet very portable microscope, to be used on the spot. So he designed his own model which was manufactured in 1893 by the well known Charles Baker's microscope firm, of High Hoborn, London, and named "The Diagnostic". Baker was chosen presumably because his firm was already producing a portable model, the Moginie Traveller's microscope. The design was so successful that the Diagnostic was produced until well into the 1920's. It went through some major restyling, as testified by the different catalogs of the time.


From left to right: Sir Ross with the first version of the Diagnostic (c.a. 1890's); the Diagnostic reviewed in the J. Royal Microscop. Soc. of 1901; the re-styled Diagnostic reviewed in the J. Royal Microsc. Soc. of 1904; the most advanced Diagnostic version in a Baker's catalogue of the 1920's.

My model is the latest version of the Diagnostic, which was produced in the 1920's. It rests on a fully foldable tripod stand, while the optical tube is mounted on a jug-handle limb carrying the pinion of the main focusing. The main optical tube can slide up and down within the sleeve carrying it, that also holds the rack of the main focusing, allowing the complete folding of the microscope when the objective lens is removed and it has also an internal draw-tube for focal length adjustments. Under the stage it carries an Abbe condenser with iris diaphragm, filter holder and micrometric screws for both centering it and moving it up and down. The double-sided plano-concave mirror is mounted on a retractable arm which can freely rotate, allowing easy oblique illumination. 

The fine focusing mounted is the coaxial Baker's new lever fine-adjustment operated by two milled heads, introduced in 1914. 


Baker's new fine adjustment, reviewed in the J. Royal Microsc. Soc. of 1914

The instrument comes in its original army-style leather case, complete with intact handle and straps. It has one 8x ocular and 2 objectives (10x and 40x) all original Baker's. I refurbished the instrument with a double rotating nosepiece marked R.&J. Beck Ltd, dating it after 1894 and an additional ocular (Watson holo 10x of the same age), which I had as spare parts. Cosmetically, the microscope is in very good conditions, with very few marks on its original black enamel and it is excellent from a mechanical and optical point of view. It is a sturdy, compact, yet very capable instrument. An ideal companion for the field microscopist.


C. Baker

Charles Baker entered the microscope business in 1851 and the firm was so successful to be present on the market until 1949, when it was acquired by the company Vickers Ltd. Originally called C. Baker, it became C. Baker & Co in 1936 and C. Baker Ltd in 1940. Having been in business for so long, Baker produced almost all types of microscopes, from the early bar-limb models, to the Jackson-Lister ones and then moving to the continental stands in the XX century. Among its most prized and elegant instruments, was the "Baker-Nelson" model, meant to compete with the "Royal" and "van Heurck" models by Watson. For more details on the firm see Brian Bracegirdle's book "Notes on Modern Microscope Manufacturers".


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