THE ANGLE OF TEACTION, ETC. 



243 



in the direction Q and Q', at right angles to i\I and 

 0' M'. Therefore the horizontal pull on the trace is 

 not in this case, a very common one, the most advan- 

 tageous, but the contrary. It is, however, evident 



Fig. 



that with the larger wheel the most advantageous line 

 of traction Q lies nearer to the horizontal line H 

 than does the line of traction 0' Q' of the smaller 

 wheel, and it is agreed on all hands that the hue of 

 traction of a horse attached to a wheeled vehicle must 

 be somewhere near the horizontal line H, so that 

 this shows that hindrances of a given height are more 

 easily overcome by a larger wheel than by a smaller 

 one, and that in exact proportion to their relative 

 heights. Nevertheless there, must he ahuays an advan- 

 tage to the motive power when it is exercised somewhere 

 between H and Q ; ajul as H can, supjjosing an 



r2 



