PROFESSOR H. B. DIXON ON THE RATE OF EXPLOSION IN GASES. 175 
the copper plate D attached to the ebonite. The whole piece could be moved to the 
right or left by a pinion working in the rack E. 
Fig. 10. 
Bmdina scrturs to 
'PiaJtinum ptat^ 
Copper strip wWv picotlTiicrri povnt 
Side view o£ one of tlie breaks. 
The tuning fork was by Koenig. It gave 100 complete vibrations per second at 
15° C. Its temperature correction was determined by Mr. R. H. M. Bosanquet in the 
Laboratory of St. John’s College, Oxford. By measuring the length of the wave 
traced by the tuning fork on the plate at different heights, a table of wave-lengths 
was constructed, giving the value of second at different heights on the plate, and for 
different lengths of swing. After measuring the distance between two marks of 
a stylus and the height of the tracing on the plate, a reference to the table gave the 
value of the distance in time. But, to make sure that the pendulum was moving at 
the same rate as when the table was constructed, a tuning fork trace was taken after 
each experiment—everything being in the same state except that the tuning fork was 
substituted for the electro-magnetic styli. From the length of the observed trace, 
compared with that given in the table, a correction could readily be applied to the 
table readings. A small correction was also made, when necessary, for the effect of 
temperature on the tuning fork. 
The distance between the marks of the styli was measured by cutting the rising 
trace 2 mm. above the datum line with a pointed style, and drawing a perpen¬ 
dicular line through the points of intersection, as shown in tig. 11. At n the upper 
stylus began to rise in the preliminary experiment, and the lower stylus at h. In the 
explosion the lower stylus was released by the breaking of the first bridge, and began 
to rise at h '; the upper stylus was released by the breaking of the second bridge, and 
began to rise at a. The distances between the lines A A' and between the lines BB' 
being measured, as well as the position of aa and hh' on the plate, the value of BB' 
