64 



Trans. Acad. Sci. of St. Louis. 



of the dark circular area around the negative terminal. 

 These lines do not terminate in the negative pin-head 

 terminal in the same manner that they originate in the 

 positive terminal. They appear distorted near the nega- 

 tive terminal, as if by a blast from that terminal. The 

 significance of this will appear later. It may, however, 

 be here stated that the conditions in this region, just 

 outside of the negative glow, are like those in the Faraday 

 dark space in the vacuum tube, although the mean free 

 path of the molecules is of course very much less. 



Canal Rays. 



The results heretofore discussed in this paper and in 

 the preceding one, suggested the idea that an insulated 

 plate of metal placed between spark terminals of the 

 influence machine should arrest the ionization of the air 

 column between them and prevent the passage of sparks. 

 This was tested by the arrangement shown in Fig. 2. 



A and A 1 are large knobs of about 10 cm. diameter, 

 having adjustable floating spark terminals a and a 1 . The 

 large knobs are metalically connected with the larger 

 knobs forming the terminals of the machine. Small spark 



