174 PROFESSOR H. B. DIXON ON THE RATE OF EXPLOSION IN GASES. 
connections were immediately adjusted as in the preliminary experiment, and the 
pendulum was again let fall. If the confirmatory ” marks passed directly over 
the “preliminary” it was a proof that nothing had been displaced during the 
experiment.* 
Fig. 9. 
In the companion experiment, which was made as soon as possible after the first, 
tlie wires from the break X were removed from BB to B'B', and the wires from X' from 
B'B' to BB. X was now the firing break. Any difierence between the two breaks 
which might affect the moment of firing was thus eliminated by taking the mean of 
the pair of experiments. 
The breaks were constructed as shown in fig. 10. The contact wms made between 
a platinum plate A and a platinum point B joined to a co^Dper strip. The platinum 
plate was fastened to a [fiece of ebonite turning on a horizontal axis; a spiral spring 
})ressed tlie plate against the platinum point until the arm C of the pendulum struck 
* Ml'. F. J. Smith Las jiointetl out that tlie dilferciice in the latencies of two electro-magnetic 
styli may he eliminated by making two experiments, and reversing the connections for the second 
experiment. I think my plan of making a “preliminary experiment” (without tiring the gases) is 
quicker. In both cases it is assumed that the latencies remain constant during the exjierimeut: the 
quicker the operation the more likely is this coiiditiou to be attained. 
