208 SIR ANDREW NOBLE: RESEARCHES ON EXPLOSIVES. 



resistance of which has been carefully determined. Attached to this plunger at I is 

 a lever, the fulcrum of which, c, is fixed to the stationary bracket of the indicator, so 

 that, when the spring is compressed, motion is given to the ends of the lever. 



Fixed to the lever are two electric magnets d, the one to record seconds, the other 

 to perfect the firing circuit. A rocking bar e is coupled up over the seconds magnet, 

 which is again coupled at the other end by a link /, thus conveying the seconds 

 beats of the chronometer to the pen tracing its path on the revolving drum. 



The revolving drum itself is of light wood ; fixed to the frame are two rods gg, 

 upon which slides the carriage for carrying the recording pen. The pen is held up 

 by a detent, which is liberated by the firing current passing through the electro- 

 magnet to which the detent is attached. There are two speeds given to the drum, 

 the first a high speed (about 40 inches per second), the second very slow, about one 

 inch per second. The drum is revolved by means of cord bands, which lead from the 

 speed gear of the motor. 



Before firing, the fast-speed cord is made to drive the drum, the slow-speed cord 

 running free ; about one or two seconds after the explosion the change speed 

 lever is raised, thereby releasing the fast cord and tightening the slow cord. The 

 fast speed is obtained approximately by watching the tachometer, but the actual 

 speed is determined by measuring the length of the second on the recording 

 diagram. The diagram is traced on a sheet of tin foil backed by paper. This is 

 placed on the drum as shown on Plate 4, the edges being joined with gum, the 

 surface being smoked black by camphor. 



The chronometer is of the ordinary marine type, but is furnished with a seconds 

 make-and-break arrangement ; this being coupled up through a relay to the pressure 

 lever, causes the recording pen to beat seconds till the desired curve is complete. 



The action of the apparatus during an experiment is as follows : 



All connections being made, the chronometer is coupled up, the pen carriage beating 

 seconds, but no mark is yet made on the recording tin foil, the pen being held by the 

 detent. The drum is started, and when it has reached the desired speed, as shown by 

 the tachometer, the button of the firing battery is pressed and the circuit is completed 

 at the beat of the next second. 



The current simultaneously releases the pen and fires the charge. As quickly as 

 possible the speed is reduced by raising the speed lever and at the same time 

 reducing the speed of the motor. The chronometer continues to beat seconds, thereby 

 giving the relation between time and pressure until the experiment is concluded. 

 The diagram is then removed from the drum by cutting through the point where the 

 pen dropped, this being the beat of the second firing the charge. The sheet is then 

 laid on a tray face up, flooded with thin varnish, and hung up to dry. 



For the purposes of these reseaches, which are specially directed to ascertain the 

 differences in the phenomena attending the transformation of explosives fired under 

 diiferent pressures, I have employed three explosives, viz., the cordite known as 



