Wheels with Broad Felloes. 667 



is fixed to a pulley, 3 inches in diameter. This pulley 

 is placed flat upon the forward axle of the carriage, 

 behind the bar of wood above mentioned ; so that, when 

 the rope is stretched by the pulling of the horses, it 

 lies in the direction in which the carriage is going. 



On the small wooden wheel, three quarters of an 

 inch in thickness, which forms this pulley, another 

 wheel, not quite so thick and 12 inches in diameter, 

 is fixed in such a way that the two wheels, attached the 

 one to the other, form but a single body, turning freely 

 on an iron pivot between two pieces of oak, which are 

 fastened by iron pins to the forward axle of the car- 

 riage. A rope, less stout than the first, is fastened at 

 one end to the larger wheel of this double pulley, and 

 encircles it (in an opposite direction, however, to that 

 of the larger rope, which is around the small wheel) ; 

 and its other end being fastened to the hook of a steel- 

 yard or circular spring-balance, the elasticity of this 

 spring opposes the effort of the horses to draw the 

 carriage, and balances it continually, and the needle of 

 the balance indicates the amount of force employed. 



Since the diameters of the two wheels, around which 

 the two ropes pass in opposite directions, are in the pro- 

 portion of I to 4, it is evident that the amount of force 

 indicated by the needle is only one quarter of that put 

 forth by the horses. 



The balance which I use is made to weigh 1 50 pounds : 

 it is therefore evident that it ought to be able to resist 

 the force exerted by the horses in drawing, until this 

 force becomes equal to a weight of 600 pounds ; but in 

 the experiments that I have made, up to the present 

 time, that force has never exceeded 300 or 400 pounds, 

 even in the jerks given to the carriage by the horses in 



