‘The mechanics’ improved sliding rule as improved and arranged by Robert Hawthorne, Civil Engineer, Newcastle-upon-Tyne. (1841)

This slide rule has been in the present owner’s family since it was brought to Australia in 1851. It comprises a two foot folding boxwood rule with a brass hinge, marked in inches and provided with tables of useful constants. There is as well a brass slide let into one side that can be used for a variety of calculations. On its back it is marked in inches, so can be used as a depth gauge or to extend the range of the rule to three feet. Its front has logarithmic scales which can be used for calculations involving multiplication, division, squares, square roots etc for the determination of areas, volumes and more complex quantities.

The accompanying instruction manual, dated 1841, explains how to make a wide range of calculations, many using constants called ‘gauge (or guage) points’ listed on the rule. An interesting feature is that some of the calculations involve reversing the slide end-over-end. The booklet has a sticker marked ‘John Cail, Mathematical Instrument Maker, Optician Etc, 61 Pilgrim Street and 45 Quayside, Newcastle on Tyne’. The manual is 80 by 134 mm with cardboard covers.

All the pages of the instruction book are available as JPEG files of length about 180kB.

These were made with a digital camera as the binding was too delicate for scanning.