Maker's Name: 
Museo di Storia della Scienza, Firenze
Where made: 
41 × 20 × 1 cm

The inventor of this piece of mathematical equipment was Galileo Galilei. Created between the years of 1595 and 1599 with a handbook for operation, Le operazioni del compasso geometrico e militare, appearing in 1606, the device was meant particularly to aid artillery men target their cannons

This is a cardboard replica of a brass original in the Museo di Storia della Scienza in Florence. The instrument makes use of a method known as line of equal parts and can be used to solve a variety of problems but is best suited to proportion problems. In using this method it became a versatile instrument and would have been used by those skilled in mathematics. At the time, Galileo’s instrument was not considered a ‘success’ due to its lack of profit even though many were sold. From a mathematical point of view it was a great achievement as many great mathematical advancements stemmed from it.

To understand the versatility of this small device we must examine the lines and properties hidden in it. Most obviously, it has a weight attached to a string, referred to as a plumb line. This most commonly was used to measure the angle of cannons but can be used as sight for different angles when building houses measuring slopes and other angles.  With the curved brace removed, allowing the hinge to operate, the device could be used as a calculator. On the front face starting from the centre working outwards Galileo’s instrument has arithmetic, geometric, stereo-metric and metallic lines. On the rear there are polygraphic, tetragonic and added lines [4]. Other useful relations that were used in his device were that of sine, cosine and tangent but these are masked in central arc.

Whilst Galileo didn’t make a fortune off this device it has become an invaluable piece in history for its combination of formula and mathematical lines and its contributions to advancing mathematical instruments. Sectors were still included in sets of mathematical instruments at the end of the nineteenth century.    

This item is part of the UQ Physics Museum Good Old days of Calculation Tour
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