142 
MINUTES OP PEOCEEDINGS OF 
In the first place, it is apparent that the distance between the axles 
never enters the question; that is to say, their distance apart does not 
affect the traction. (If it was granted that the surface of the road 
upon which the wagon was destined to travel was, in its length, uni¬ 
formly wavy—as in Fig. 2—the distance apart of the axles might be 
suited to the particular length of wave, but to no other. Thus, it would 
obviously be bad to have the distance apart of the axles the same as 
the distance, ab , from one wave to the other, because in that case both 
the fore and hind carriage wheels would be ascending at the same 
time, causing a maximum traction, and at the next instant both des¬ 
cending, causing a minimum. Manifestly, in this case, the best length 
between the axles would be \ab 3 so that one pair of wheels would 
always be descending, and therefore their traction decreasing, when 
the other pair were ascending, and therefore their traction increasing.) 
In the next, that the distribution of the weight over the axles should, 
in a “ lock-under - ” wagon, be as the radii of the wheels. Practically, 
rather less than this should be thrown upon the fore-wheels, because 
the obstacles to their traction are usually greater than to that of the 
hind wheels, due to their first meeting the obstacles, and, in passing 
over them, reducing their height for the hind. In an “ equirotal” 
wagon, the same reason for throwing rather less weight on the fore 
than on the hind wheels holds equally good: setting, however, this 
point aside, it appears from the formula that in such a wagon it is a 
matter of indifference how the load is distributed over the axles; and 
this would practically be true was it not for the yielding nature of 
most roads permitting the weight to sink the wheels into them, which 
must occur to a greater extent if the weight is thrown mainly upon one 
pair of wheels— i.e. upon two points of support, instead of distributed 
more equally over four. 
Equation (A) may be made more simple by supposing the direction 
of the traction to be parallel to the ground : thus making (3 = y, 
p __ AU’.fiV U B A (1 + 1*?) (cos* y . ir * + sin* y . tv**) — 
__ _ — “ C'£\(I + Jgj — AC £ »\p*.' 
sin y {CB 2 (1 + /* 2 ) (7F+ W) - AC* . /x 3 . IF) 
+ ‘ CB 3 (1 + fx 2 ) — AC 3 . /x 3 
The resistance which an obstacle of even small height offers to 
traction deserves to be noticed. It is measured, as already shewn, by 
the increase which for the instant it adds to the slope of the ground. 
Suppose, for illustration, a 5-ft. wheel to meet an obstacle T V in. in 
height. By equation ( C ), 
sin e = ’0645, 
and e = 3° 45' (very nearly). 
