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- G.— ENGINEERING. 129 
Beary and they ran at very moderate speeds, such as 200 revolutions 
per minute. About 1883 Daimler set himself to produce an engine with 
_ much lighter working parts which should run at a far higher speed, five 
_ times as fast, or more, and should use for fuel an oil so volatile that a 
_ carburettor would serve to charge the incoming air with combustible 
_ vapour. After successful trials with a bicycle, he applied his motor, 
in 1887, to drive a car on the road. That was the beginning of a new 
era in locomotion. The world discovered in Daimler’s petrol engine an 
appliance such as it had not possessed before—a light, convenient, inexpen- 
sive prime-mover, yielding amounts of power which were ample for road 
vehicles, easy to start and stop and regulate, demanding little attention 
and no particular skill. Before long it gave city streets an altered charac- 
ter and country roads an unsuspected value. Man acquired a new 
“mobility which changed his notions of distance and of time. In due course 
the petrol engine also achieved the conquest of the air. At the end of 
1903, only a few days after Bramwell’s death, the brothers Wright took 
their first flight in a motor-driven aeroplane. It is the petrol engine 
that must bear the responsibility—the grave responsibility—of having 
made it possible for man to fly. 
The era of the road-motor began with Daimler’s experiment of 1887, 
but a good many years were to pass before it took the dominant position 
it holds to-day. The horse was already in possession, and did not yield 
without a struggle. That sensitive animal had a frank dislike of the 
horseless car. To meet his objections our legislators—not much wiser, 
it would seem, then than now—ordained for mechanically-driven vehicles 
a pace not exceeding 4 miles an hour, and required each of them to be 
in charge of three persons, one of whom should carry a red flag in front. 
Not till 1896 was the Red Flag Act repealed. The sinister emblem has 
one, and the horse has nearly gone, too. But engineers will not let his 
memory perish. Thanks to the initiative of James Watt, they treasure 
his name in one of their most necessary words. The horse may become 
little more than an instrument of sport or an excuse for betting, but it 
is safe to say the horse-power will never die. 
_ Ihave yet to mention another milestone in the history of internal 
mbustion. It was soon recognised that the efficiency of the action 
pended on the extent to which the combustible mixture in the cylinder 
compressed before it was fired; the more compression the greater 
s the subsequent expansion in the working stroke, and consequently 
igher was the efficiency. But a practical limit was set by the danger 
the mixture would automatically ignite before the proper time if 
‘much compression were attempted. Users of petrol engines know 
$ danger well; often they try to diminish it by introducing what are 
ed dopes. It was not in petrol engines, however, but in heavy oil 
es that Rudolph Diesel initiated an epoch-making change about 
Instead of compressing a combustible mixture, he compressed 
air alone, bringing it to a very high pressure, and thereby making it 
0 hot that when the charge of oil was forcibly injected at the dead-point 
re was instant ignition. This escaped all risk of pre-ignition and greatly 
‘augmented the efficiency of the action, as a thermodynamic consequence 
the very high temperature at which the fuel gave up its heat. To 
1931 K 
