. CALCULATING MACHINES. 



of a quotient v has been fixed between the arms, the plate must be 

 turned until the one arm is brought to a factor c, the product ^ c will then be 



read on the other arm. This arrangement admits of the scale being made as 

 long as may be necessary by breaking it into lengths, without rendering the 

 instrument inconvenient. In the exhibited instrument ten circles are used, 

 by which means the scale attains a length of five meters, and is accurate up 

 to 10 Q 00 . In using the instrument care must be taken to mark the number 

 of each scale circle, which can be fixed by small sliding buttons. The 

 number of the circle on which the result is to be read is found by the same 

 rules as the characteristic of a logarithm, on the supposition that the ten scale- 

 circles form a graphic table of logarithms of all the natural numbers, the base 

 of the system being 



38. Arithmetical Disc, a very simple calculating machine, 

 with accompanying description. Prof. Prestel, JEmden. 



39. Calculating Machine, of the last century. 



The Royal Gewerbe Academy, Berlin (Director Prof. 

 Reuleaux}. 



This calculating machine formed part of the legacy of Hofrath Beireis, 

 the well-known physicist and chemist in the 18th century, and is very similar 

 to the calculating machine, No. 36. 



40. Tide Calculating Machine. 



Sir William Thomson, 



41. Pascal's Calculating Machine (1642). 



Conservatoire des Arts et Metiers, Paris. 



42. Fetroff's Arithmetical Apparatus. 



M. Petroff, Master at the School, Kalouga. 



43. Arithmometer, with measuring apparatus, and the full 

 size skeleton of the square metre and cubic metre, folding up by 

 means of a hinge. Frere Memoire Piron. 



44. Counters and Speed Indicators. 



T. R. Harding and Son. 



(a.) Counters with reciprocating motion, as applied to marine and 

 stationary engines. 



Counters with rotary motion, suitable for shafting, printing, and other 

 machinery. 



Small counters -with rotary motion applicable to spinning machinery and 

 various other purposes. 



Speedometers or pocket counters for ascertaining the speed per minute of 

 spindles or quick running machinery up to 10,000 revolutions per minute. 



(6.) Counters actuated by pneumatic and electric apparatus at a distance 

 from the motion to be indicated. 



(c.) Speed indicators, showing by the height of a column of mercury the 

 actual speed, at any moment, of engines and other machinery. 



45. Model of Gas Meter Counting Machine. 



Council of King's College, London. 



