Some years ago, a friend lent me a small set of old microscope slides which his family owned. They were an interesting selection of slides from known late 19th century makers.
One anonymous slide though I was particularly intrigued by, as it was a slide of a tiny 'engineering' item. It looked like a ball-bearing but was only 1.5mm across! I never found out what such a tiny item might be used for, so perhaps some knowledgeable folk out there could enlighten me.
I didn't have photography facilities when shown the slides, so the details were taken from my notes and illustrated with scans of my notebook drawings.
The slide was unlabelled and undated. If contemporary with the microscope and other slides it was with, it dates anywhere from the late 19th to early 20th century, but could be later.
It's a standard 3x1 inch size slide but 2 mm thick. Rather than using a deep cell mount, a circular hole with flat base had been ground out of the slide, internally blackened and the subject mounted in the centre. A coverslip flush with the slide surface protects the subject.
The details shown above were as observed with a 40x stereo microscope. The overall diameter of the item was ca. 1.5mm and looked like a ball-bearing with three balls within. I recall the item was not brass coloured so possibly made of steel, faced with a metal cover sitting in a rim in the casing, with central hole. The metal cover didn't allow the ball diameter to be measured, but from the total dimensions the balls are ca. 0.6mm in diameter.
My engineering knowledge is scanty so perhaps I can ask some naive questions:
Is this item as it appears, i.e. a ball-bearing? If so, if the slide dates to late 19th or early 20th century, were such bearings quite common and what were they used for; perhaps a clock or other fine mechanical movement? Or was it just an exercise in 'micro-engineering' for demonstration purposes?
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Acknowledgements: Thanks to Christopher Redding for loaning me the slides in 1987.
Footnote: In a subsequent web search, I found a fascinating page, Desktop Type Micro-factory, on the website of the Japanese National Institute of Advanced Industrial Science and Technology, which describes the manufacture of modern ultra-miniature bearings. The measurements I think are in microns, and their drawing would thus show a bearing with an external diameter of 0.9mm (cf 1.5mm in the item above) enclosing ca. six balls where each is 0.2mm in diameter (cf 0.6mm above) - so an even more impressive feat of micro-engineering!
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