574 I Trials of Traction-Eiigijies at Wolverhampton. 
At 1450 feet slijipinci; again took place, and stones had to be used; at 1500 feet 
efl'orts were made by putting saclis under to get the wheels to bite, but 
such efforts were useless. A chain was then attached, but this would not do. 
It was then determined to take off the portable engine ; with this reduced load 
of 13 tons nett behind the " Sutherland," or 23 tons 4 cwts. gross, including its 
■weight, a start was made, but even with this load the wheels slipped a good 
deal ; however, the summit was reached at last. It may be taken that the limit 
of adhesion of these cast-iron wheels, with a gross load of 23 tons 4 cwts., was . 
reached upon an incline of 1 in 20: the resistance due to gravity would, there- 
fore, be 1'17 tons ; the resistance due to the traction upon a level 'GG ; together 
1"83 tons. The insistant weight being 7J tons, the ratio of adhesion is "244, 
in lieu of the "35, with the cellular wheels of " Aveling," and the "45 with the 
indiarubber wheels. It must be borne in mind, however, in comparing the 
iron wheel to the " Aveling " with the iron wheels of the " Sutherland," and 
then with the indiarubber wheels, that the "Aveling" wheels were 6 feet in 
diameter, while those of the " Sutherland" were only 5 feet. 
The road trials appeared to sliow that, with a road in good 
order as this was (it should have been stated that it appeared to 
be formed of a mixture of flint, iron slag, and a little granite) 
the indiarubber tyres have a decided advantage over iron in 
tractive force ; there is no doubt that thej have the advantage of 
giving an elastic support to the whole machine. These advan- 
tages, however, are obtained at an addition to the first cost, in 
the case of such an engine as the " Sutherland," of 250?., or fifty 
per cent, of the cost of the *' Sutherland " with iron wheels, the 
price of the engine under these circumstances being 500/. 
Assuming the truth of the statements made by the advocates of 
the indiarubber tyre, that they may be used for years when pro- 
tected with steel bands without appreciable wear, so that the 
cost of maintaining these tyres should not be a very heavy item, 
it nevertheless becomes a question how far their superiority in 
tractive force warrants a purciiaser in going to the original greater 
outlay. This is a question which experience alone can authorita- 
tively settle : but we are inclined to think that for road traction 
it may be worth the while of the proprietor to go to the expense 
of these tyres. It is, however, a question upon which we cannot, 
in the absence of longer experience, venture to pronounce a 
decided opinion. Our business was to award the prize in 
Class XVII., which was to be given " for the best agricultural 
locomotive engine applicable to the ordinary requirements of 
farming." 
We had, therefore, to judge of the merits of the engines 
when used to replace portable engines, as a mere implement for 
driving farmyard machinery, of their merits when used as loco- 
motives upon the high road, and of their merits when used as 
locomotives upon farm roads, or upon the surface of fields where 
there were no roads. 
In this latter respect the indiarubber tyres most signally failed 
