ON GASEOUS EXPLOSIONS. 203 
vessel of the size of the combustion chamber, and it must have occurred 
to many that, were it not for this fact, it would hardly be possible to 
work internal combustion engines at reasonably high speeds because 
the ignition would be too slow. It now appears that this is wholly, or 
almost wholly, due to the fact that the gas in the engine is in turbulent 
motion. 
Simultaneously with the experiments by Dugald Clerk, described 
in the last paragraph, Professor Hopkinson (with the assistance 
of his pupils, Messrs. Miley and Peache) carried out some measure- 
ments of the effect of turbulence on heat-loss and inflammation 
phenomena in a closed-vessel explosion. A cylindrical vessel, 1 foot 
in diameter by 1 foot long, was used and was lined with copper strip, 
the rate of heat-loss being measured by a record of the rise of electrical 
resistance of this strip. A small fan was mounted in the centre of the 
vessel and comparisons were made of the result of exploding the same 
mixture, first with the fan at rest, and second when the fan was driven 
at a speed of several thousand revolutions per minute. These experi- 
ments also showed the great increase in speed of inflammation conse- 
quent on the motion of the gas. Taking a mixture of 10 per cent. of 
coal-gas and 90 per cent. of air, the time from ignition to maximum 
pressure with the gas at rest is about 0'13 second; with the fan running 
at 2,000 revolutions per minute this time was reduced to 0°03 second, 
and at a speed of 4,500 revolutions per minute to 0°02 second. The 
effect on heat-flow was also very marked. At maximum pressure, with 
a 10 per cent. mixture, the rate of flow of heat was approximately 
doubled when the fan was running at a speed of 4,500 revolutions per 
minute, the mean temperature of the gas in the two cases being the 
same (about 1600° C.). It is interesting, however, to note that at the 
higher temperatures reached with a 15 per cent. mixture—say at 
2000° C.—the heat-flow from the gas was not materially altered by 
the turbulent motion produced by the fan. This is doubtless due to the 
fact that at such temperatures radiation is an important agent in the 
transfer of heat, and this would probably be unaffected by the motion of 
the gas. 
_ For the application of the results obtained with the closed vessel 
and the fan to the gas-engine, it is necessary to get some measure of the 
amount of turbulence remaining in the latter at the end of the com- 
pression stroke. Mr. H. J. Swain, under the direction of Professor 
Hopkinson, has made some measurements during the past year bearing 
upon this point. It is hoped that full details of these experiments, and 
of those cited above, will be published in the course of the next few 
months, and the results only need be given here. The method used 
‘was to determine the rate of loss of heat from a platinum wire mounted 
in the combustion chamber of a gas-engine, the wire being heated by 
an electric current. Within moderate limits of temperature the heat- 
loss from such a wire is proportional to the temperature difference 
between it and the surrounding gas. The ratio between heat-loss and 
temperature difference is a measure of the effective conductivity of the 
gas, and depends upon its temperature, density, and state of motion. 
‘If the first two factors are the same, then the effective conductivity 
