130 SECTIONAL ADDRESSES. 
force the fuel in, he at first employed an auxiliary supply of still more 
highly-compressed air, but this plan is now less common than the simpler 
one of using a high-pressure pump, which delivers the oil in a spray of 
exceedingly fine drops. The essential feature of the engine is that the 
fuel does not enter the cylinder until the air there is highly compressed 
and the working stroke is about to begin. It is this feature which has 
made the Diesel engine the most efficient of all known means of obtaiming 
mechanical work from the combustion of fuel. When I say the most 
efficient, I am using the word in its thermodynamic sense ; other factors 
obviously enter when you come to consider questions of mechanical sim- 
plicity, of suitability for a particular purpose, or of cost. 
As a small-power prime-mover in situations where electric supply is 
not available, such as country houses, farms, or isolated workshops, the 
convenience of the internal-combustion engine has, in fact, led to its 
almost universal use in preference to steam. 
We have still to speak of how, for larger uses, the steam-engine has held 
its own during this half-century of change. Before doing that, however, 
it may help us to realise the other side of the matter if we imagine our 
prophet of 1881 brought back to earth so that he may see for himself in — 
what measure his expectations have been fulfilled. 
He will come, of course, by aeroplane, and on the way the pilot will 
tell him of the part which the internal-combustion engine played in the 
War; of submarines, and road-motor transport, and tanks and aircraft. 
He will be told of Zeppelins and air-raids, of the horrible superiority of — 
attack over defence that characterises modern war. He will learn how ~ 
prodigiously man has increased his power to kill his fellows and destroy 
their works. The old gentleman will be saddened to think that the world 
owes this to engineers, and especially to the internal-combustion engine. — 
It will grieve him to reflect that the island safety of England has departed, 
never to return. On the other hand, he will be told of air-mails to India 
and Australia and the Cape, and it will interest him much to learn that 
the engine which is bringing him so swiftly and comfortably to earth 
weighs no more than a couple of pounds per horse-power, and that engines — 
of much the same type, but lightened and tuned to the uttermost for 
racing, can develop more than a horse-power for every pound of weight. 
He will hear, perhaps with less enthusiasm, of speed records by air and 
sea and land. amazing records which are set up only to be broken. “ Brief 
life is here our portion’ might be said of the records, and also, alas, of 
many of the record makers and record breakers. As he approaches 
London our aerial voyager will note the highways thick with motor- 
cars, coaches and lorries, and will wonder for a moment what has’ 
happened to the railway shares he left behind, doubtless selected as a 
secure investment of the terrestrial fruits of his industry and thrift. For 
in Bramwell’s time there were still people who practised these now 
exploded virtues, and there were even Chancellors of the Exchequer 
who encouraged them. 
We may imagine that instead of landing at Croydon the pilot brings 
him over the river and the docks, where he may see big motor-ships like 
the Nelson liners arriving with their frozen or chilled cargoes. One 
of his pet bits of engineering was mechanical refrigeration, and he will 
