1915] 



on Gaseous Explosions 



295 



Fig. 23 shows a section of this valve, from which it will be seen 

 that a small additional valve T is provided at the centre of the main 

 valve A, which carries within it the platinum loop of a Callendar 

 platinum resistance thermometer. The loop is shown at P, and the 

 wires leading to it are carried through the valve stem and pass at B to 

 the necessary recording instruments. In this ingenious device the 

 valve carrying the resistance thermometer is reciprocated by a separate 

 cam gear, and it is opened at the particular period of the stroke 

 during which temperature is to be taken. It is closed before explosion 

 takes place, so that the temperature of suction or compression can be 

 measured at any period of the cycle, and yet the platinum loop is 

 moved away before the cylinder is filled with flame. By this device 

 it is possible to obtain accurate measurements of temperatures during 

 any part of the compression stroke, and indeed during most parts of 



Fig. 23. 



the expansion and exhaust stroke. The thermometer valve cam 

 operates quite independently of the charge inlet cam, so that the 

 ordinary action of the inlet valve A is not interfered with. In order 

 that the wire may assume change of temperature rapidly, it is 

 necessary that it should be thin ; and, accordingly, to read temperature 

 for any particular point, other arrangements are required which 

 measure resistance for a minute period of time. To accomplish this. 

 Prof. Dalby has invented an ingenious percussion contact-maker, 

 which makes contact just at the instant when temperature requires to 

 be measured. The galvanometer measurement is given by a succession 

 of small currents, one for each succeeding stroke. In this arrange- 

 ment it is necessary to keep up consecutive ignitions when experi- 

 menting as to temperature. Callendar and Dalby found the suction 

 temperature to vary with the conditions of running from about 95° C. 

 on lio^ht load trials to about 125° C. at maximum load, with the 



