GASEOUS COMBUSTION AT HIGH PRESSURES. 



315 



taken, with slight modifications, from Prof. PETAVEL'S memoir on "The Pressures of 

 Explosions.""" 



The gauge is screwed into the explosion chamber by means of the thread, U. A 

 gas-tight joint is formed by the ring, D, on the manometer pressing against a flat 

 ledge in the enclosure. The end of the gauge from D to E fits well in the. walls of 

 the explosion chamber, and the joint is thus protected from the direct effect of the 

 explosion. The spring, S, about 5 inches in length, is tubular in shape, and to 

 prevent any buckling it is made to fit closely the cylinder, in which it is contained, 

 in two places e l and c. 2 . The spring is fixed at its other end, Z, being held in position 

 by the nut, K, whilst at its other end it is free and supports the piston, P. 



The mirror, M (which in our experiments was of silvered glass with a focal length 

 of about 2'5 feet), is attached to a lever, and at the outset of an experiment is kept in 

 the zero position by means of the stretched piano wire (gauge 25), W ; adjustment of 



Fig. 15. 



the zero is effected by means of the screw, V. The distance between the knife edges 

 of the mirror holder in our experiments was one thirty-second of an inch. 



The sources of light employed by us was the crater of an electric arc in which the 

 carbons were at right angles, and the beam was reflected by the mirror on to a 

 sensitive photographic film fixed on to the drum, A, of the chronograph (fig. 15), also 

 designed by Prof. PETAVEL (loc. cit.}. 



This drum (diameter = 8'8 cms.) which was usually rotated at a constant speed of 

 between 200 and 600 revolutions per minute by means of an electric motor, was 

 anclosed in a light-tight aluminium casing, BB, provided with a longitudinal slit, the 

 width of which could be adjusted to suit the particular experimental conditions, and 

 which could also be closed when required. An electrically-controlled tuning fork, 

 giving 100 to 200 vibrations per second, was used as a time indicator ; the fork being 

 so placed that each vibration momentarily interrupted the light falling on to the 

 photographic film, thus producing a dotted record on the resulting pressure curve. 



VOL. ccxv. A. 



'Phil. Trans.,' 1905, A, vol. 205, p. 363. 

 2 T 



