Details and Image
|Date||Scale Length||Area of Use
|Linear||Lalanne / Glass||Lalanne||France||Glass & paper||Ext. 1852||25 cm||General Calculations
Notes: "The Lalanne glass slide rule was invented in 1851 by Léon Lalanne, and was sold by (and possibly made by) L. Hachette, a bookseller in Paris. An English language instruction book for the Lalanne slide rule says that they were made by Elliot & Sons in London, but that could mean the English version was made there. This one is marked entirely in French. The unique feature of the Lalanne slide rule is that the scales and slide are made of paper or card, and the whole thing is sandwiched between two pieces of glass. The two pieces of glass are held together by tape that wraps around the edges. The markings on the rule were all done by hand, probably on a master that was somehow reproduced. The faint guide lines for the height of capitals, numbers, and lower case lettering can still be seen if you look closely. The Lalanne has scales equivalent to a Mannheim slide rule, making it one of the earliest ‘full function’ general purpose slide rules sold. An instruction book dated 1852 has been found, and that is about it for hard evidence of production dates. So few examples of this rule exist today (only a handful are known) that there is unlikely to ever be enough data to answer all the questions this rule brings up. The rule is signed, “L. L.”"