PEOFESSOR H. B. DIXOE OX THE RATE OF EXPLOSION IX GASES 173 
into the base of the cylinder. The tube C was then filled with electrolytic gas 
through the tap G, the air escaping at E. On firing the gas in C by the firing wires 
the explosion travelled to F, and there set off the detonator in the middle of the 
cyanogen mixture. The explosion thus started was propagated through the tube B, 
into the explosion tube which it traversed to the end. 
Fig. 8. 
G 
= 34 = 
B 
I 
3F A 
B ridge 
2vTv 
To Expiosi/m 
Part III.— Chronogra'pliic A'pparatus. 
The arrangement of the chronograph and electrical connections are shown in fig. 9. 
The chronograph, made by Messrs. Elliot, consisted of a heavy pendulum carrying a 
smoked glass plate. The electro-magnetic styli used were made by Pfeil, of Berlin, 
and by Mr. F. J. Smith,"'' of Trinity College, Oxford, to whom I am greatly indebted 
for several of these instruments. In most of the experiments recorded in this paper, 
one of Pfeil’s instruments and one of Mr. Smith’s were employed. These two were 
chosen out of several, for the great constancy of their latent period, and for the 
sharpness of their action. The styli were attached to an upright bar on a heavy 
iron stand, with three pointed feet. The bar could be tilted back on two feet 
and exactly replaced. 
At the lowest point of its swing the pendulum acted on two breaks, X and X', 
which by a rack and pinion could be brought exactly in a line. By bringing the 
pendulum slowly against the uprights the position of the two breaks could be 
adjusted so that they were broken at the same instant. 
In the preliminary experiment the wires wmre arranged as shown in the figure, 
except that the wires to the firing battery were detached at C'C’, and the wires from 
hh, h'h' to the two bridges were not connected. The stylus S was put in circuit 
through a resistance HR, and the break X ; the stylus S' was put in circuit througli 
a resistance R'R' and the break X'. On letting the pendulum fall the two styli were 
released, and registered their marks on the moving plate. The resistances RR and 
RR' were now removed, the firing battery and coil put into circuit at C'C', the wires 
from hh and h'h' attached to the two bridofes, and the wires from the coil attached to 
the firing piece. The pendulum, being again let fall, broke the primary circuit of 
the coil on striking X', causing a spark to pass between the platinum wires in the 
firing piece. The flame travelling down the tube broke both bridges in turn, and 
the styli connected with them registered their marks on the moving plate. The 
* ‘ Phil. Mag.,’ 1890, p. 377. 
