668 On the Advantage of Employing 



shying (which all the care of the driver could not 

 always hinder), nor in the shocks caused by obstacles 

 met by the wheels. 



Since the motion of a horse is never perfectly uni- 

 form, the force exerted by the horses in drawing a car- 

 riage must of necessity vary at every step. This causes 

 the needle, which indicates at any moment the force 

 actually employed at that moment, to oscillate contin- 

 ually, and sometimes with such rapidity that the eye 

 can scarcely follow it. However, notwithstanding this 

 continual oscillation, it is not difficult in ordinary cases 

 to determine with sufficient accuracy the mean force of 

 traction. We have only to take what seems to be the 

 mean between all the oscillations ; leaving out of account 

 those which are the result of the shying of the horses, 

 as well as those which are caused by foreign objects, 

 as bits of stones, etc., which the wheels sometimes en- 

 counter on all roads. 



In order to make this paper more satisfactory and 

 more useful, I must give a detailed description of the 

 different kinds of wheels used in my experiments. 



The wheels of my carriage which I had next before 

 the last were made in Munich. They are very light, 

 and very much worn. Their tires, which were origi- 

 nally an inch and three quarters broad, are so much 

 worn and rounded at their edges that it is difficult to 

 say how broad they really are now ; and- this causes the 

 wheels to slip continually, especially on a worn pavement. 

 I have used them but little in my experiments, for 

 fear they would crush under the weight of the carriage. 



My last wheels were made in Paris, by a very skilful 

 workman (M. Gamier, living on the Rue Neuve-des- 

 Mathurins). I have had them already more than two 



