THE ANGLE OF TRACTION, ETC. 217 



nearer to the ground — from the moment the animal 

 stretches itself out and laj^s itself into the collar ; and 

 the amount of this lowering will of course vary with 

 the pace, being greatest at full gallop, and also with 

 the amount of effort required. 



The French artillery gives the trace an inclination 

 of only 1 P with the horizon, and the rule seems to 

 have been deduced from a series of experiments 

 made at Metz by General Berge in 1816, at the time 

 the new system of artillery carriages, copied from the 

 English, was about being introduced."* This officer 

 found that the greatest effort was exercised by all 

 horses — strong, weak, and medium — when the trace 

 was inclined between 10° and 12** with the horizon, or 

 on an average IP, and this greatest effort exceeded by 

 more than i that obtained with the perfectly horizontal 

 trace. Applying a trigonometrical calculation to this 

 fact, it will be found that this angle of 11° corresponds 

 with the supposition of the horse's shoulders being 

 pressed on to the ground by a force equal to i 

 the horizontal effort exerted. Following out this 

 indication. General Berge next tried the effect of 

 weighting the shoulders artificially in different pro- 

 portions, and found that by putting 100 kilogrammes on 

 the horse's shoulders he obtained the same effort under 

 an angle of between 6° and 7° that tlie unweighted 

 horses gave at IP; and that weighting with 50 to 60 

 kilogrammes under the latter angle gave an inferior 

 result to that given by the greater weight (100 kilo- 

 gi'ammes) under the lesser angle (6° to 7°). 



But all these experiments having been made on a 

 fixed machine, and not on a movable carriage, were 



* Migout et Bergery, * Theorie des AflFuts et des Voitures 

 d'Artillerie. ' 



