202 REPORTS ON THE STATE OF SCIENCE.—1912, 
obtained in this manner with that following a normal ignition would 
show the effect of turbulence on heat-loss. While the experiment did 
not give any very clear indication on this poifit, it was the means of 
bringing to light a matter of perhaps greater importance. Clerk 
found that the result of damping down the turbulence was to retard 
the rate of inflammation of the gas to a very remarkable extent, so 
that the character of the diagram was completely altered. Two of 
Clerk’s diagrams are reproduced (see figs. 1 and 2), from an inspection 
of which the importance of this point in the working of gas-engines 
will be appreciated. If ignition be delayed until the combustible mix- 
ture taken into the engine has been compressed and expanded: twice 
and then again compressed, the period of inflammation is about two 
Fig. 2.—Ordinary ignition, a to b, takes 0033 second ;_ trapped ignition on third 
compression ; line a’ to 6’ takes 0°078 second ; mixture in both cases, 1 vol. 
gas, 9°3 vols. air and other gases. 
and a half times that of a normal ignition in which the gases have some 
turbulent motion. The diagrams shown, figs. 1 and 2, were taken 
by an optical indicator from an engine of 9 inches diameter cylinder 
and 17 inches stroke when running under full load at 180 revolutions 
per minute. The engine was fitted with two electric igniters; one 
operating at the charge inlet-valve at the back of the combustion 
chamber, and the other operating at the side of the cylinder close to the 
piston. In fig. 1 the back electrical ignition was used, and in fig. 2 
the side igniter was in operation. It has been noticed more than once 
that the period of inflammation in the gas-engine is considerably less 
than that obtaining in an explosion of a similar mixture in a closed. 
