1!)()7.] on Flame in Om and Petrol Motor ii. 507 



invented a cycle of operations, which gave in the same cy Under, one 

 power impulse at each revolution. This cycle is now known as the 

 Clerk cycle, and it comes next to the Otto cycle in order of number 

 of engines now running in the world. I have here two sections, 

 showing the operation of the Clerk cycle. Its characteristic consists 

 of open ports at the out end of the stroke, which are over-run by 

 the piston. The pressure in the cylinder rapidly falls to atmosphere, 

 and a charge is forced into the motor cylinder at low pressure, from 

 a low pressure pump, or displacer cylinder. This displaces the 

 exhaust products remaining in the cylinder, and furnishes the fresh 

 charge, which is compressed on the return stroke into a space at the 

 end of the cylinder. This charge is ignited, and in this way a 

 l)ower impulse is obtained for every forward stroke of the piston. 

 A second cylinder is required, in order to supply the charge. The 

 second cylinder, however, is very Hght in construction, both as to 

 the cylinder itself, the piston, and the connecting rod and cranks 

 driving it. 



I have here a small engine, built to my designs on the Clerk 

 cycle twenty-four years ago. The German authorities requested me 

 to present it to the Munich Museum, to form a Unk in the history 

 of the internal combustion motor, and I did so some years ago, but 

 the authorities there have kindly lent it to me for the purpose of 

 this lecture. The engine is sectioned, so that I can show you the 

 movements and action of the two pistons. 



In the early days of these engines, great difficulty was found in 

 ol)taining regular consecutive ignitions at a sufficiently rapid rate. 

 Although Lenoir used the electric spark for ignition, it was not then 

 in a sufficiently reliable form to produce a good commercial engine. 



TJje ignition device is a most important detail, which proved too 

 much for many of the earlier inventors. Whatever may be the skill 

 and energy devoted to the construction and cycle of the engine, it 

 remains a useless mass of metal, requiring power to move itself, 

 rather than furnishing power to set other machines in motion, until 

 an effective ignition is found. The early Otto engines had a flame 

 igniter, of which I show two sections. That ignition depended on 

 the principle of filling a pocket in a valve-port with coal gas, 

 igniting a lower surface of that gas in contact with air in the lower 

 part of the port, and carrying the flickering flame thus produced 

 quickly from communication with the external atmosphere, where it 

 was lighted, to communication with the interior of the cylinder. 

 I have here a little experiment, which shows at once the nature of 

 the Otto flame igniter. Here is a spirit lamp, and here a gas jet. 

 I Hght the spirit lamp, take tlie glass cap, place it over the jet, allow 

 the gas to stream in to fill the cap, move the cap over, ignite it at 

 the spirit lamp, and pass it back, when you see that the gas jet can 

 be ignited Ijy the flame carried by the cap, although I have placed 

 the lamp and the jet nearly twelve inches apart. The Otto flame 



