Thursday, September 3, 2009

Can you calculate this?

Can you do math calculations in your head? How about long division on paper? Have you forgotten the multiplication tables above 5? Well then I'll bet you don't have any idea how to use a slide rule. Much less a Thatcher's Calculating Instrument.

This calculator is in the Bremerton Navy Museum. A little web searching found this description of a similar instrument in the Powerhouse Museum:
Cylindrical slide rule, metal / paper / wood, designed by Edwin Thacher, New York, United States of America, 1897-1907

'Thacher's calculating instrument' is a cylindrical slide rule that can be used to calculate results by adding and subtracting logarithms. The machine consists of a cylinder with wooden handles at either end. The cylinder has been covered in glossy paper that is printed with log scales; it rotates inside a series of twenty brass bars that are also covered with gloss paper printed with log scales. Along the front of the cylinder there is a brass bar to which a sliding holder for a magnifying glass is fixed. The machine is mounted on a rectangular wooden base that has a label printed with instructions for use fixed to it.
Designer: Thacher, Edwin
Designed in: New York, USA
Designed date: 1871

Read more:
Under Creative Commons License: Attribution Non-Commercial

Statement of significance:
This is a very accurate desk-top slide rule of a type used to perform calculations between 1881 and the 1960s, when electronic calculators became available. Slide rules are analog devices that the user manipulates to add and subtract the logarithms of the numbers involved in a calculation.

The first cylindrical slide rule, with extra long logarithmic scales to provide greater accuracy, was introduced by Irishman George Fuller in 1879. Edwin Thacher's 1881 design set new standards in accuracy by pushing computations to four digits. This feat was accomplished by dividing up a very long linear rule into equal lengths and arranging the pieces around a cylinder with a barrel slide. Sometimes referred to as a 'squirrel cage' slide rule, its use of both rotary and longitudinal movement gave the rule an effective length nearly 40 times greater than that of an ordinary slide rule.

By 1897 the New York company of Keuffel & Esser had taken over production of Thacher's slide rules and, in a curious footnote to history, misspelled his name 'Thatcher' for the entire life of their production.

Significance Statement by Geoff Barker, March 2007

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