Mr Hunter's Account of an Improvement on the Odometer. 45 



The object of my proposed improvement is to register this 

 step by the introduction of a third wheel A of 102 teeth, to 

 be turned by the same perpetual screw, and upon the same 

 principle that the index fixed to C points upon the scale of B 

 to the number of revolutions performed by C ; another index 

 fixed to B will show, upon the scale of A, the revolutions of 

 B ; but the revolutions of B are simultaneous with those of 

 C, and, therefore, no account is to be taken of those of B as 

 long as they are the same as those of C, or, in fact, until af- 

 ter C has performed 100 revolutions, having the index of B 

 pointing upon A also to 100. At the end of the next revolu- 

 tion, however, the index of C will point to of B, and 

 that of B to 101 of A ; and at this point the improvement be- 

 gins to take effect. 



The of B is equivalent to 101 ; and I find that when- 

 ever B is less than A, 101 must be added to B ; we there- 

 fore have the instrument pointing to 101 of A, or 101 

 of B, and of C. A and B, therefore, are still the same, 

 and the calculation is 101 revolutions of C, or 10,100 turns 

 of the measuring-wheel ; and at this point the two-wheeled 

 instrument has completed the performance of its duty, and is 

 ready to recommence. 



At the end of the next revolution the instrument will point 

 to of A, 1 of B, and of C. Here we find a differ- 

 ence of 1 between B and A, which difference of 1 stands for 

 10,100 ; and to it we add the 1 of B, which stands for 100, 

 and we have 10,200 which we know to be the number of 

 turns of the measuring-wheel ; accordingly, for the future, 

 the following formula must be resorted to : B — A X 10,100 + 

 100 B-|-C= turns of measuring-wheel ; and whenever B is less 

 than A, 101 must be added to B, because, in fact, B may be 

 supposed to continue its scale after 100, instead of commenc- 

 ing anew at 0. 



This last wheel I have recommended to be made to measure 

 6{ij feet, because that is J^ of an English chain for square 

 measure, and the same, or T ^ of a furlong, for long measure ; 

 but there is no practical objection to its being made of any 

 size that may suit the convenience of the person using it. 

 By means of these three wheels, the Odometer mea- 



