NEW CALCULATOR. 



755 



hand is forced to follow, and carries the hour hand with it. By the hidden" 

 arrangements the hands are dependent one upon the other, but remain 

 independent in movement. If they be moved backwards or forwards they 

 will return automatically to their respective places^ and if turned quickly 

 round the minute hand will return to the proper minute, and the hour hand 

 to the hour. 



The mechanism is simple and ingenious ; the principle, however,, is not 

 absolutely novel, and before M. Robert applied it many attempts had been 

 ma-de to move indicators by the machinery they themselves contained. But 

 M. Robert has succeeded in adapting the idea beneficially and usefully, 

 giving it a practical as well as an elegant shape. 



A NEW CALCULATING DIAL. 

 The small instrument herewith illustrated (figs. 882 and 883) is very 



Fig. 882. A new calculating dial. 



Fig. 883. Reverse view. 



serviceable for calculators, and its size adapts it for the waistcoat pocket. 

 It can be used to calculate by addkion, subtraction, multiplication, and 

 division. Logarithms can be found, and the powers and roots of numbers 

 even trigonometrical calculations may be made by its aid. We need not go 

 into any details regarding the principle of the little " circle." Such explana- 

 tions are only wearying and unsatisfactory at best. The principle is, simply 

 stated, the theorem that the logarithm of the product of two numbers is equal 

 to the sum of their logs. The size of the dial will of course regulate the 

 length of the calculation. The instrument depicted permits of calculation 

 to three figures with exactitude, M. Boucher, the inventor, hopes to succeed 



