376 



MR. \V. T. DAVID ON THE RADIATION IN 



case. By measuring the radiation emitted by the hot 'gaseous mixture (by means of 

 a bolometer protected by a plate of fluorite) he shows that these results are in a large 

 measure, if not entirely, due to this radiation being reflected back by the polished 

 walls and reabsorbed by the gas, this reabsorption of the radiation being ultimately 

 realised, at any rate in part, as pressure or translational energy. 



No other work has been done on radiation in gaseous explosions. Some interesting 

 measurements, however, have been made on the radiation emitted by flames and by 

 heated gas. Those made by Prof. CALLENDAR on flames and by Prof. PASCHEN* on 

 heated CO are particularly interesting and will be referred to later on in this paper. 



Description of Apparatus. 



The explosion vessel used in these experiments consists of a cast-iron cylinder, 

 30 cm. in diameter and 30 cm. long, on to which are bolted two end plates. It is 

 shown in section in fig. la together with the bolometer holder H. 



Fig. 1. 



The bolometer was cut into the form of a grid from a circular disc of platinum 

 about mm. thick, weighing 0'25 gr. per sq. cm., and had, therefore, a thermal 

 capacity equivalent to O'OOS gr. of water per sq. cm. (the specific heat assumed to be 

 0*032). Its resistance measured about O'llS ohms at 15 C. The temperature 

 coefficient was measured and found to be 0'0036. The bolometer was mounted on a 

 hollow cylinder of wood (W in fig. l) and was pushed into the gunmetal holder H, 

 which carried at its inner end the plate of diathermanous substance. The holder H 

 was screwed into a boss on the end cover of the vessel and was tightened up with the 

 lock nut L. 



In the experiments described in the first part of this paper the bolometer was 

 placed close up to the diathermanous plate, so that all the radiation from the hot 

 gaseous mixture, which was transmitted through the diathermanous substance, fell 

 on its blackened surface. In order to measure the amounts of radiation absorbed by 

 the bolometer it was necessary only to measure its rise of temperature. This was 



