THE ANGLE OF TRACTION, ETC. 213 



wards to press it against or into the ground, so in pro- 

 portion as it comes to be applied further and further 

 away from either of these two directions that is to 

 say, the perpendicular line up and down the more 

 power of rolling the wheel forwards would be acquired. 

 In other words, the trace should act horizontally, sup- 

 posing the wheel to move on a perfectly level and even 

 surface ; because the horizontal line lies more remote 

 from the perpendicular than any other, being at right- 

 angles with it. 



And many good practical authorities who have had 

 much experience tell us the same thing ; amongst 

 others, the author of the ' Handy Horse-Book,' who 

 thinks that to make " the draught as easy as possible, 

 the axles [of a carriage] ought to be on a level with the 

 trace -hooks, or point of traction, or as nearly horizontal 

 as possible with the traces and their place in the leg 

 of the hames." * 



On the other hand, we have practical authorities 

 -who say, " The best disposition of the traces in draught 

 is when they are perpendicular to the collar ; when the 

 horse stands at ease the traces are then inclined to the 

 horizon, at an angle of about 15; but when he leans 

 forward to draw, the traces should then become nearly 

 parallel to the road." f 



Before going further, let us observe here on the modi- 

 fication that the mathematical rule is made to undergo, 

 from the moment you leave the level (horizontal) plane, 

 and get on to inclined planes ; for we see that the trace 

 which was at first-starting parallel to the horizon be- 

 comes parallel to the road, and therefore forms less than 



* ' The Handy Horse-Book,' p. 73. 



f ' The Artillerist's Manual,' by Major Griffiths. Sixth edition 

 p. 150. 



