Art. XII. — The Calculimetre. 

 By James J. Fenton, F.S.S. 



[Eead July 11, 1889.] 



The Calculimetre is a civcvilar measure of French make 

 for performing approximate arithmetical and trigonometrical 

 calculations. It consists of a flat disc of metal about the 

 size of a watch, which can easily be attached to a chain and 

 carried in a watch pocket. On one face, there are the two 

 principal scales — one movable, the other fixed — for per- 

 forming the ordinary rules of multiplication, division, and 

 proportion; also a third scale for finding the squares and 

 square roots of numbers. On the reverse face may be 

 instantly found, by means of a movable arm, the logarithms 

 of numbers, and the sines and tangents (the latter being 

 under 45°) of angles. 



This instrument is, of course, based on the principle 

 of Gunter's line, i.e., a scale divided logarithmetically, 

 but marked with the natural numbers only, and has the 

 advantage over the ordinary carpenter's and other similar 

 slide-rules of convenience and portabilit}^, and a readier 

 application to arithmetical calculations, besides having the 

 additional scales for trigonometrical calculations. The 

 arithmetical scales are about the same length as in the 

 ordinary slide-rule, and, with good observation, results 

 with the first three figures of a result can often be closely 

 ascertained. 



Some time ago, I brought before the notice of this Society, 

 Fuller's Calculating Slide-rule,^ which will readily give 

 accurate results to the fourth and sometimes to the fifth 

 figure. In that ingenious instrument, however, the scale is 

 of great length, being no less than 41 ^^ feet, it being 

 drawn in a spiral form round a cylinder ; whilst in the 

 more portable calculimetre the scale is only 64 inches in 

 length, and of course cannot give the more extended 

 results which may be obtained with the invaluable rule of 

 Professor Fuller. But in cases where rough approximations 



* Vide paper read 10th September, 1885. Two of these iustruments have 

 been in constant use in the office of the Government Statist for a long time 

 past, and have proved most invaluable for statistical computations. 



