480 



31r. Warren De La Bue 



[Jan. 21, 



Fig. 17. 



a second, and it is necessary, therefore, to have recourse to special 

 means in order to detect it, which I will describe. 



The current from the battery of 2400 cells is made to pass through 

 the primary of an induction coil, and then through a vacuum tube (No. 



142, Fig. 11 in the plate — the figure 

 is copied from a photograph ob- 

 tained in 2J seconds) containing a 

 residue of carbonic acid at a pressure 

 of 0*4 millimetre. The arrange- 

 ment is shown in Fig. 18, where 

 T T' is the vacuum tube connected 

 in circuit with the primary of coil 

 819 ; Z A the battery, on the A 

 side connected with fluid resistances 

 F R, F R', and wire resistances 

 amounting in all to a megohm. On 

 the Z side is shown a condenser C 

 connected through a fluid resistance 

 F R" with the Z pole. The termi- 

 nals of the secondary wire of the 

 induction coil are connected with a 

 sensitive Thomson galvanometer. 

 If there is any intermittence in the 

 current through the tube, an eflect 

 will be produced on the galvano- 

 meter under certain circumstances, 

 that is, provided the rise and fall 

 of the current occur in unequal 

 periods. I will now make connec- 

 tion with the battery ; you perceive 

 that there is a deflection of the gal- 

 vanometer to the left on making 

 contact ; I will now allow the spot 

 of light to come to rest, and then 

 break contact, and there is a deflec- 

 tion in the reverse direction, that 

 is, to the right. The first is called 

 the inverse current, the last the 

 direct current. I will now send the 

 current again through the primary 

 of the induction coil and thence 

 through the tube, but in the first 

 instance I will short-circuit the 

 secondary current so that the galva- 

 nometer may not be disturbed when the connection with the battery 

 is made ; now that the strata are perfectly steady, I will allow the 

 induced current to go through the galvanometer by removing the short- 

 circuit plug, and you see that there is a slight permanent deflection 



