﻿Ignition of Gases by Sudden Compression. 79 



perfectly certain, or at least as certain as any mathematical 

 or logical proposition. On the other hand, it' it is meant that 

 the law will be to me and to others an equally satisfying 

 interpretation of all future experience, then I am not 

 absolutely certain ; I am only as certain as I can be about 

 anything in the future. And it must be noticed that nothing- 

 can make me more certain. If I were predicting something 

 about a single future occasion, I might in the .course of time 

 become more certain; for that future occasion might some day 

 become past. But if, as in the case of a scientific law, I am 

 predicting something about all future experience, then, since 

 the future is indefinite, no amount of additional experience, 

 converting finite portions of the future into the past, can 

 make me more certain; for there will always remain as much 

 future as before. Such uncertainty as there is in the 

 proposition is inherent in its nature ; if it were absolutely 

 certain, it would not be the same proposition. 



VIII. Experiments on the Ignition of Gases by Sudden 

 Compression. By H. T. Tizaed and D. R. Pye *. 



[Plate I.] 



I. TN a previous paper f, it was shown that when a mixture 

 JL of a combustible gas or vapour with air was suddenly 

 compressed, explosion miglit take place after an interval the 

 duration of which depended on the temperature reached by 

 the compression. It is known that below a certain tempera- 

 ture, called the ignition temperature, no explosion, and no 

 very appreciable reaction, takes place under these conditions ; 

 and the experiments referred to showed that just above the 

 ignition temperature, the delay before explosion occurs may 

 be of the order of one second in certain cases, while — in the 

 case of hydrocarbons and air — the delay at a temperature 

 some 50° above the ignition temperature was very small. 

 It was pointed out that the observed ignition temperature 

 must not only depend on the properties of the combustible 

 substances, but also on the conditions of experiment, and 

 particularly on the rate of loss of heat from the gas at the 



* Communicated bv the Authors. 



t H. T. Tizard, "The Causes of Detonation in Internal Combustion 

 gines." Proceedings of the N.E. Coast Institution of Engineers and 

 Shipbuilder, May 1921. 



