1007.] on Flame in Gas and Petrol Motors. 517 



that the indications are not quite clear, but the oscillation is un- 

 doubted. This oscillation is very different from the usual indicator 

 oscillations which vitiated the earlier experiments. 



Professor Hopkinson has also made another interesting experi- 

 ment bearing on the same point. He has ignited a mixture of gas 

 and air at the top end of a long vertical tube, 6 feet long, by about 

 7 inches diameter. The indicator was placed at the bottom end, 

 and the diagram was produced which I show you. This diagram 

 shows a smooth, rising line until maximum pressure is approached. 

 Then the indicator gets into violent movement, and it will be 

 observed that on the cooling line the oscillation lasts, with gradually 

 diminishing intensity, for quite a long period— not far short of a 

 second. Combustion is evidently proceeding during this particular 

 oscillation, because just at the terminating point of the oscillation it 

 will be observed that the cooling curve has a break in it, a sort of 

 hump. At that hump, as I understand it, the ordinary laws of 

 cooling begin to have effect ; but up to that point combustion appears 

 to be proceeding in the long tube. 



At present, I have a number of experiments in hand on engines 

 of different sizes, with the new optical indicator, and hope to get 

 accurate figures, both as to specific heat, and continued combustion 

 and heat flow through the cylinder sides. 



Experiments have been made by Messrs. Holborn and Austen on 

 the specific heat of air and carbonic acid by another method entirely, 

 and there is reason to hope now, that, between the various experi- 

 ments which, to my knowledge, are now progressing in this country 

 and on the Continent, the whole question will be cleared up in the 

 next few years in a satisfactory manner. 



As engineers, we are vividly interested in the progress of know- 

 ledge as to the working fluid, Ijecause, without that knowledge, it is 

 not possible to attain the ultimate practicable heat conversion by 

 means of the internal combustion motor. At present, however, the 

 internal combustion motor is by far the most efficient means of con- 

 verting heat into mechanical work. 87 per cent, conversion has 

 been achieved, and so far as present indications point, it will be 

 possible to make an engine converting over .")0 per cent, of the whole 

 heat given to it into mechanical work. This has been made possible 

 only by the study of the properties of flame, not only on the 

 physical, but on the chemical side, and on the mechanical side, using 

 devices of sufficient delicacy and rapidity to deal accurately with 

 large volumes of a very difiicult working fluid. The mean tempera- 

 tures attained by the working fluid in many engines is as high as 

 1800° C. It has been found that attempts to measure the tempera- 

 tures in the cylinders by platinum thermometers always result in the 

 melting up of the platinum wire. 



Flame, as I have already said, has required over one hundred 

 years' effort by engineers and scientific men to enable it to be handled 



