260 REPORTS ON THE STATE OF SCIENCE. 
as possible; secondly, with it blackened over; and, thirdly, after it had 
been protected from direct contact with the flame by means of a plate 
of rock-salt fixed in front of it. It was found that the rate of rise of 
temperature of the blackened strip during combustion and the early 
stages of cooling greatly exceeded that of the polished strip, and that the 
difference between them was, roughly, the same as the rate of rise of 
temperature of the strip protected by rock-salt. It appeared that the 
amount of heat lost to the walls of the vessel by radiation up to the moment 
of maximum pressure was, with a 15-per-cent. mixture by volume of 
coal-gas and air giving a maximum temperature of 2150° C., of the 
order of 5 per cent. of the whole heat of combustion, and there was 
evidence that the radiation continued for some considerable time after 
maximum pressure, until the temperature of the gas had fallen to © 
1400° C. The experiments are not yet sufficiently advanced to give a 
quantitative basis for the correction of volumetric heats obtained by 
explosion experiments, but Hopkinson considers that they establish the 
fact of a material amount of radiation at the moment of maximum pressure 
and during the first stages of cooling. 
Apart from their bearing on the determination of volumetric heats, 
these results, if fully confirmed and proved to be due to radiation and not 
to differences in roughness of surfaces or other secondary causes, will 
raise interesting questions as to the origin of the radiation and as to the 
state of the gas at the moment of maximum pressure. Comparing the 
two explosions, one with the bright lining and the other with the blackened 
lining, it seems to be established that the maximum pressure and the 
maximum temperature are the same; on the other hand, the experiment 
with the bolometer would seem to show that more heat has been lost 
in the one case than in the other; and therefore the energy of the gas 
enclosed in the bright lining is greater than that of the gas enclosed in 
the blackened lining, though the temperatures are the same. If this be 
the fact, there must be some want of equilibrium at this moment. ._Many 
chemists, including Bunsen and Professors Smithells and Dixon, have 
held the opinion that radiation from a gas, at any rate at temperatures 
such as can be obtained in an explosion, can only go on as a result of 
some sort of chemical or quasi-chemical action. According to this view, 
the want of equilibrium at the moment of maximum pressure must 
be due to incomplete combustion, and the continuing radiation after 
maximum pressure must be regarded as evidence of continued chemical 
action. This view as to the radiation from a gas is, however, not generally 
accepted, and the existence of radiation, therefore, cannot be regarded as 
conclusive evidence of continued combustion. If it be assumed that com- 
bustion is complete at the moment of maximum pressure or very shortly 
after it, then the want of equilibrium at this moment disclosed by the 
experiments must be ascribed to purely thermal causes. The most obvious 
explanation in such a case would be that the translation and vibrational 
energies of the molecules have not attained their equilibrium proportion. 
Since the temperatures in the two explosions with bright and blackened 
linings are the same, the translational energies, which alone determine 
temperatures, must also be the same. It is conceivable, however, that 
the energy represented by rotation or vibration of the molecules may be 
greater in one case than in the other, 
