TRACTION. 
477 
TRACTION. 
[No. II.] 
BY 
MAJOR W, KEMMIS, R.A. 
In order to calculate tlie load which a horse may fairly be called 
upon to move, it is necessary, first, to lay down the average speed at 
which he is required to travel, and the average nature of ground over 
which he has to pass. 
As pointed out in a previous paper on Traction,"* * * § the average nature 
of ground which field artillery has to manoeuvre upon may be con¬ 
sidered to be that which opposes an average obstacle or resistance to 
rolling whose height is equivalent to a slope of 6^°. 
The average pace of manoeuvre is the “ trot, regulated with reference 
to the slowest horse,which may be taken as meaning a speed of 
7 miles an hour for horse artillery and 6 miles an hour for field 
batteries. 
A good draught horse, it is considered, moving at the former speed, 
can exert an average% tractive force of 70 lbs., and at the latter a force 
of 82 lbs.—the duration of labour being from 4 to 5 hours. § 
The tractive power of a team is not directly proportional to the 
number of horses in it; in fact, it has been asserted that no more than 
six horses can usefully be employed in a team, if much speed is 
required. 
Assuming, however, that the full power of the individual units is 
obtainable from a team of six horses, when well trained and well 
* “Proceedings, R.A. Institution,” Vol. IX. p. 138. 
f “ Manual of Field Artillery Exercises,” 1875. 
$ “ He adapts himself admirably to his work, increasing or diminishing his efforts according to 
the variations of draught—resting himself, as it were, and acquiring vigour where his utmost 
strength is not called for ; and thus becomes enabled to make exertions far beyond his average 
strength where any obstruction is to be overcome.”—Youat on the Horse. 
§ Rankine, in his “ Manual of Civil Engineering,” gives a tractive force of 64 lbs. for a speed of 
7\ miles per hour, and 96 lbs. for 5 miles per hour, in each case working 4 hours a day. 
Tredgold, in his work on Railways, gives 83 lbs. for a speed of 4 miles per hour and 62*5 lbs. for 
5 miles per hour, in each case the duration of labor being 6 hours ; and states that if the hours of 
labor be lessened, the velocity may be raised much higher. 
Youat concludes that when 6 or 8 miles per hour is required, the day’s work should be 5 or 
6 hours and the draught 80 to 100 lbs, 
