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An unexpected strike of serendipity
|Here is an unassuming wooden slide rule, missing its glass cursor. Or so I thought at first, when I bought it for a pittance from a nondescript antique shop. Later I realized that there is no wear to indicate that it ever had a cursor, and I grew suspicious. Searching the web for "Gravet Lenoir", the maker's name, revealed so little information that I had to search Usenet and write the one guy who seemed to know about this... and I learned that I had a real "find", a 19th century slide rule worth 30 times what I paid for it. The cursor, by the way, isn't missing: it hadn't yet been invented at the time!||
Click photo to enlarge
Click a photo to enlarge
As you can see in the close-up, this slide
rule was meticulously crafted in Paris; the address tells us that this
happened sometime between 1827 and 1867. Monsieur Lenoir, a pioneer of
precision slide rule manufacturing in France, was dead by
then; but his partner Gravet had kept the name in order to bank
on Lenoir's well-deserved reputation. In those days, you see, making
precision instruments wasn't a matter of raising the capital and
buying the equipment; you had to perfect your own manufacturing
techniques from scratch, and a good instrument was a precious
This slide rule has an archaic arrangement of scales known as a "Soho" configuration: three 2-cycle logarithmic scales and a fourth single-cycle scale, with the slide bearing the same scale twice. Later slide rules would have a better arrangement, but lacking the hairline cursor, which is necessary to move readings vertically across the slide, Gravet was forced to use the system we see here.
More info: to learn about antique Slide Rules, join the Oughtred Society. Its journal (which is paper based) has many scholarly articles about these matters, and covers Gravet and Lenoir in its spring 2002 (Vol. 11, No. 1) issue.
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