Eesearclies on 3fodern Explosives. 



225 



trolled by adjustable vanes. The rate of descent of the plate in the 

 experiments was one inch in 2 J seconds, or equal to four-tenths of an 

 inch for every second of time. 



Fig. 2. 



In using the apparatus, a datum line is first traced, and this is done 

 by letting the plate fall with the galvanometer at rest, the circuit being 

 closed, when the spot of light traces a continuous vertical line at one 

 edge of the plate. The plate is then brought back to its original posi- 

 tion and re-started on its descent. After it has fallen a short distance, 

 in order to make sure it has acquired a steady rate of motion, the 

 explosive is fired and the thermo-couple in the bomb is in consequence 

 heated, and the current generated deflects the mirror of the galvano- 

 meter, and therefore the spot of light, horizontally and proportionately 

 to the temperature attained by the couple ; and then, as cooling sets in, 

 the original position of the spot of light is gradually resumed. 



The result is recorded as a curve, which shows the combined move- 

 ments of the spot of light and of the photographic plate. 



Fig. 3 shows one of the plates on which three records were succes- 

 sively taken.. In these three separate experiments, couples of different 

 thicknesses, but with the same charge and kind of explosive, were 

 used. 



