1902.] on Auto-Cars. 117 



tricity, with the aid of an induction coil and a commutator— into the 

 details of which I do not mean to enter to-night — by which a small 

 spark is passed at the right moment between two platinum points in 

 the inside of the cylinder and so explodes the mixture. [Induction 

 coil and commutators were shown.] 



These are the general principles upon which the gas engine 

 works. What remained to be discovered before it could be applied 

 to road engines was some means of making a suitable gas on the 

 road. Ordinary gas you could not use, because you could only carry 

 it in a carriage by having it compressed into strong and very power- 

 ful cylinders, which were necessarily very heavy. If any accident 

 should happen, and if by any chance your compressed gas got out, 

 very disastrous results would follow. But the difficulty was solved 

 by using the vapour of a volatile oil which could be safely carried 

 and made gaseous from time to time as required. Hence " petrol,' ' 

 which is the essence of " petroleum," and extremely inflammable, is 

 generally used. But alcohol or vapour of benzoline can be used 

 effectively. This is passed through what is called a carburettor ; a 

 certain regulated quantity being brought from your tank in order 

 that you may first get the gaseous vapour which is to be mixed with 

 the air. There are various ways in which this is accomplished. 



It is obvious, as I said before, that a third question will occur to 

 you — is it not very dangerous to have an explosion when you are 

 carrying a quantity of a substance giving off an inflammable gas ? 

 That difficulty is got over by the vapour from the essence being 

 passed through small holes or through a piece of very fine wire gauze, 

 and we then have absolute certainty that no flame will go back past 

 that point to the store of inflammable liquid. A piece of wire gauze as 

 you see has this effect, that a flame does not pass through. It is really 

 a succession of very small tubes, so small that the combustion cannot 

 be maintained, and the flame cannot establish itself beyond the gauze. 

 That is the origin of the old Davy lamp for the safety of miners. 

 [Lamp shown.] A lamp covered with gauze in this way can never 

 set fire to an explosive mixture. In the suction-stroke of the piston 

 vapour is drawn off from the carburettor, much as a lady's scent 

 sprinkler draws off and sprays out scent when the india-rubber bulb 

 is pinched, the only difference being, that in the one case the air is 

 forced past and in the other it is sucked past the orifice. 



The carburettor having done this duty, the gas is let into the 

 cylinder, mixed with the air, and compressed, and we get our explo- 

 sion and our motion, and, having got that, we have to deal with it 

 according to reason, because you see you cannot possibly have an 

 effective explosion except when the cylinder is closed up. Accord- 

 ingly we have to use valves, so that when the explosion comes 

 nothing goes out at the entrance at which the gas and air come in. 

 The best illustration I can give is that of the ordinary bellows. 

 There is a little hole in the bellows and a little piece of wood work- 

 ing loose when you open the bellows but closing tight by the com- 



