572 
Trials of Traction- Engines at Wolverhampton. 
holdincr, but were mucli inclined 
to slip. Tlie "Sutherland," 
however, succeeded in getting 
up the 1 in 20, butnot without a 
good deal of slipping. When the 
1 in 18 was reached it was clear 
that this load had ftiirly over- 
powered the indiarubber. The 
weight upon the driving-wheels 
of the " Sutherland " was 7s 
tons, the gross load 43 tons, the 
inclination 1 in 20; making, 
therefore, 2-15 tons as the effect 
of gravity in drawing back the 
train : to this must be added 
the tractive force required to 
move 43 tons upon a level. We 
had no means of ascertaining 
this, as we were not jirovided 
with traction dynanometers of 
sufficient power; but referring 
to General Morin's experiments, 
and taking, as a fair mean ap- 
jtlicable to the circumstances 
of the case, l-35th as the trac- 
tive force required, then there 
must be added 1'23 ton, making 
3'38 tons as the total tractive 
force exerted by the indiarub- 
ber wheels, the weight upon 
them having been 7i tons, as 
before stated ; so that the ratio 
of friction of the steel-shoed in- 
diarubber-tyred wheels appears 
to be '45, the load being taken 
as unity, or very close upon one- 
half of the insistant weight. 
The " Sutherland " was then 
set to change its wheels for the 
iron wheels of article 2150. 
While this was being done, 
Aveling's 10-horse power engine 
being on the ground, it was 
thought a good opportunity to 
test the tractive force of that 
engine. Its wheels, as has been 
already stated, have cast-iron 
rims, convex, but with a sort of 
cellular i)attern on them ; their 
diameter is 6 feet and their 
■width 1 foot 6 inches, of which, 
however, only the central por- 
tion bore upon the road, which 
was in good hard order. The 
load with which the engine 
started was, in waggons, &c., 
behind it, 26 tons ; its own 
