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William Ladd chain driven large microscope 1850-60



William Ladd's fusee chain large microscope

This is a large bar-limb first class microscope, 37 cm tall in its upright position and with a base of 15 x 13 cm. Coarse focusing is controlled by two knobs on the main limb, while fine focusing is attained by a spring-loaded micrometric screw mounted on the main tube. The upper plate of the stage can be rotated 360° or detached entirely, while the stage itself has X- and Y-axis movements controlled by two knobs on the right side of the stage. Under the stage a removable sliding plate carries a pinholes rotating wheel diaphragm, which could be eventually substituted with a condensing lens (not included). It comes with its mahogany case, two live boxes, a 3/4 inch objective with RMS thread and two top-hat oculars (4x and 10x). The field lens of the Huygenian eyepiece is incorporated in the main optical tube, as was common in the instruments of that age, suggesting that originally the top element of the ocular was fixed (also suggested by the presence of a thread on the inner side of the tube where the original top lens was screwed in. So, very likely the two oculars have been added later (even though they are of roughly the same age). I have refurbished the instrument with a 1/6 inch objective and another top-hat ocular (8x), which I have acquired as spare parts. Inside one of the drawers there was a Arthur Cole original slide with a dark-ground deep mount of mixed foraminifer shells, plus a box of XIX century glass coverslips.

This microscope is unsigned, but it can be firmly attributed to the London maker William Ladd, based on the following considerations:

- The coarse focusing and the X-; Y- axis movements of the stage are not based on the standard rack-and-pinion design, but are controlled by tiny fusee chains.

This was a patented design by William Ladd, who first introduced this particular movement in a microscope presented at the Great Universal Exhibition in London in 1851.

 

 




The fusee chains controlling the coarse focusing and the stage movements of my microscope (top) compared to the original drawings describing the new Ladd's chain driven movements published in the book "Practical treatise on the use of the microscope", by the famous microscopist John Quekett in 1855 (bottom).

- The overall design of the microscope is identical in every detail to the large model produced by Ladd in the 1850's as illustrated in the Quekett's book "Practical treatise on the use of the microscope (1855) and on the Illustrated London News (1852).

 




Frontispiece of Quekett's book of 1855 and inside illustration of the Ladd's microscope presented at the Great Exhibition in London in 1851.




Image of the Ladd's microscope exhibited in London in 1851 from the magazine "Illustrated London News" of 1852.


 

My instrument is also identical to the Ladd's microscope in the collection of the Museum for the History of Science in Oxford




Microscope by W. Ladd, London 1850s. MHS, Oxford

A Ladd microscope of the same kind is also reproduced on the frontispiece image of the very popular book "The microscope" by Jabez Hogg.




Frontispiece of the Book "The microscope" by J.Hogg 2nd ed. (1856) showing a Ladd's microscope.

The fusee chain mechanism was found to be superior in terms of smoothness of movement with respect to the usual rack and pinion. However, it did not have great diffusion. It continued to be used by Ladd on his most famous "Student" model and has been also adopted by the London maker R.J. Beck on his "Universal" students' microscope model in the 1860's, but it soon disappeared.

 




R.J. Beck's "Universal" model with fusee chain focusing (images from an internet auction; used for illustrative purposes only)




Frontispiece of Ladd's 1861 catalogue, showing his new "Student" model.

 

The rack and pinion design continued to be perfected and became the standard (still used today). One limitation of the chain driven mechanism was the tendency of the chains to break and to loose tension with use. It must be noted that the chains of my microscope are still intact, an uncommon case due to their intrinsic fragility. The stage movements are still perfectly functioning with amazing smoothness, while unfortunately the indentations on the small pinion controlled by the knobs for the coarse focusing, upon which the chain rolls up, weared off with use, so that the main focus should be adjusted by hand. This, however, does not prevent at all the use of the instrument which still delivers beautiful images. The microscope is in very good conditions overall, retaining >80% of its original lacquer; a nice and not so commonly found example of one of the early Ladd's instruments.

 

William Ladd

William Ladd operated in London from 1846 to 1884 (when he died). According to his advertisements, he was providing microscopes to several Government institutions and Universities (among them Oxford and Cambridge). Historically, he contributed the original chain driven mechanism for focusing and he is also remembered for the very innovative and elegant design of his "Student" microscope. After 1884, his shop was taken over by Harvey & Peak, which traded instruments until 1909. For more details on the firm see Brian Bracegirdle's book "Notes on Modern Microscope Manufacturers".

 


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