326 



THE POPULAR SCIENCE MONTHLY. 



certain number of millimetres traversed by the style in the vertical 

 direction. The course of the style, which corresponds to a kilometre, 

 ought to be experimentally determined for each vehicle, for the perim- 

 eter of wheels is not always the same. But it is clear that, if from 

 each kilometre-stone to another we obtain five millimetres, for example, 

 for the course of the style, this length will always be found to be trav- 

 ersed each kilometre by the same vehicle. Our apparatus is then a 

 measurer of distances, and dispenses with the necessity of attending to 



HeurtsO h 



a- 



l>> 



.: 



i. 



>. 



Fig. 7. Tracings of the Odograph : a, rapid coach with (stoppages ; b, slow coach ; c, gas 

 meter, frequency of turns of the wheel; d, curve of the turns of a clock wheel-work with fly. 



the existence of kilometre-stones ; it enables the distance traversed on 

 any road whatever to be estimated, and even when there is no beaten 

 track. Thus in a journey of discovery we may measure the distance 

 traversed by a cart. To remain in the conditions of ordinary life, have 

 we not sometimes in the country a choice of two or three roads to go 

 from one place to another ? To know which is the shortest we appeal 

 to the watch, as if the least duration of a walk corresponded to the 

 least distance. The odograph will give in this respect very precise 

 information. 



There are again a great number of questions which we ask daily 

 without being able to solve them. Does such a draught-horse go 

 quicker than such another ? Does this trot better to-day than yester- 

 day ? By increasing the ration of oats do we increase speed ? Com- 

 pare the slope of two curves of rates, and you will have the reply to 

 all these questions without being obliged to make special ex])erinients 

 on a measured road, watch in hand. 



It is not only to the speed of vehicles that the registering apparatus 

 applies ; it traces, though with less precision, the rate of progress of 



