378 



MR. W. T. DAVID ON THE RADIATION IN 



suspension, having a period of alx>ut ~$ second. The field was produced by means of 

 an electromagnet, magnetised nearly to saturation value. 



For recording the pressures a Hopkinson Optical Indicator was used. 



The mirrors on both the indicator and the galvanometer were connive, and by 

 means of them two spots of light were reflected on to a photographic film, revolving 

 at a known speed, care being taken that the two spots of light were on a line at 

 right angles to the direction of rotation of the film. By this means both the rise of 

 temperature of the bolometer and the pressure of the gas were recorded at the 

 same time. 



The inflammable mixture was introduced into the Vessel in the following way : 

 The vessel was first exhausted by means of an air pump, and the quantity of coal-gas 

 required to give the mixture a certain strength was admitted ; air was then allowed 

 to rush in bringing the pressure up to atmospheric. The gas when let in to the 

 explosion vessel at low pressure quickly diffused throughout the whole space, and the 

 air afterwards rushing in at high velocity thoroughly stirred up the mixture. To 

 make certain that the mixture was homogeneous, it was allowed to stand for about 

 half-an-hour before firing. This is a method of mixing recommended by Mr. DUUALD 

 CLERK.* 



In all the following experiments the mixture was fired by means of an electric 

 spark at the centre of the vessel. 



Fig. 3 is a print from an actual record taken during the explosions of a 'J'8-per-ctMit. 

 mixture of coal-gas and air when the bolometer was protected by the plate of fluorite. 

 Curve P gives the rise of pressure (measured downwards from the atmosphere line P ) 



0-6 0-56 0-5 0-45 '4 "35 '3 '25 "2 "15 '1 '05 0-00-9 '8 



-^ second 1 '0 



Fig. 3. 



and curve G the galvanometer deflection (measured upwards from the zero line G ). 

 On the pressure curve P, 1 mm. deflection corresponds to a rise of pressure of 4 ll>s. 

 per sq. in., equivalent to a rise of temperature of 80 C.t On the curve G, showing 

 the galvanometer deflection, 1 mm. corresponds to a rise of temperature of the 

 bolometer of 1'36 C., or, since the thermal capacity of the bolometer was equivalent 



* 'The Gas, Petrol, and Oil Engine,' vol. I., p. 156. 



t Temperature before firing 14 C., barometer 760 mm. of mercury, contraction of volume on 

 combustion 2 5 per cent. 



