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Radiation, although the subject of study for many years, is not yet thoroughly understood. The investigations of von Helmholtz 30 years ago showed that from 10 to 20 per cent of the total heat of combustion is due to radiation; but flames burning in the atmosphere show different characteristics from those subjected to a change of density in a combustion-chamber and the same conclusions do not apply. The possibility of a non-luminous flame's causing loss of heat during and after combustion was first noted by Professor Callendar in 1907. The principal theory as to the source of radiation is that it is due to the vigorous vibration of the gas molecules formed on combustion, and that, like the high-frequency radiations producing light, it is caused by chemical rather than thermal action. It has been shown that radiation emanates almost wholly from the carbon dioxide and the water molecules.

The authors present in this paper an explanation of gaseous detonation based upon what are considered incontrovertible laws, and show by the functioning of these well understood natural laws that gaseous detonation is a phenomenon that does not require any hypothetical assumptions to account for its existence. The physical conditions that must exist within an enclosed container when it is filled with an explosive mixture of gases and these gases are ignited are stated and analyzed mathematically, and an application of this analysis is made to the internal-combustion engine. The apparatus and the procedure are described inclusive of photographs and charts, and it is shown how the formulas can be applied (a) for constant throttle, by varying the temperature of the entering charge and (b) for constant temperature, by varying the throttle opening and the compression-ratio. The results are illustrated and discussed in some detail.

The various methods employed to measure detonation or fuel knock in an internal-combustion engine, such as the listening indicator, temperature and bouncing-pin, are discussed and the reasons all but the last cannot be employed to give satisfactory indications of the detonation tendencies of fuels are given. The bouncing-pin method, which is a combination of the indicator developed by the author and the apparatus designed by Dr. H. C. Dickinson at the Bureau of Standards, is illustrated and described. In this method the evolution of gas from an electrolytic cell containing sulphuric acid and distilled water measures the bouncing-pin fluctuations in a given period of time. The accuracy of this method of comparison is brought out in a table. The qualities that a standard fuel must possess are explained and the objections to a special gasoline are pointed out.

In the case of the internal-combustion engine, where virtually every separate portion of explosive mixture behaves differently, the usual thermodynamic interpretations of the pressure-volume indicator-card, as applied to steam engineering, have little value. In internal combustion, the pressure-volume diagram is of value only as an expression for the product of the force exerted upon the piston-top times the distance through which the piston moves. The paper (Indiana Section) begins with the fundamental phenomena and develops from them a diagram such that each fuel-mixture particle can be properly exposed for analysis during the process of combustion. This is termed the pressure-volume-quantity card, and it is described in detail and illustrated. An extended consideration of its surfaces follows, inclusive of mathematical analysis.