267 



As a final study three mg. of racluim bromide were placed beneath the 

 points, in an attempt to change the form of discharge, as described by 

 A. E. Garrett^ for discharges between blunted wires. The radium, which 

 was contained in an unstoppered glass tube, was held by an ebonite rod so 

 that both a and /? particles might reach the air in the path of discharge. 

 No effect was observed except that which could be produced by a glass rod 

 in the same position. 



SUMMARY OF EESULTS. 



A summary of the results, as given in this and the previous report, is : 



(1) The positive stream between the points for a spark or brush 

 discharge was deflected by a magnetic field as low as 1,000 gausses, and 

 both positive and negative streams for glow, spark and brush discharge 

 were deflected by a magnetic field of 6,400 gausses. In all cases the 

 direction of deflection was in accordance with electro-dynamical laws. 



(2) In most cases a change of type of discharge, and an increase of 

 potential between the points was caused by excitation of the magnet. 



(3) The direction of the photographed stream for a spark discharge 

 as it leaves the point is the same as the visible direction of the spark. 



(4) The size of the stream at tiie points (measured with a microm- 

 eter microscope between the outer edges of the central dark band) is 

 independent of the potential between the points. 



(o) The stream waj? deflected b,v an air current, the negative being 

 deflected more than the positive. 



(G) The stream for the richer spark (i. e.. for the higher speeds of 

 r!ie nKicliine) increased in width as the distance from the point increased, 

 while the stream for the glow discharge retained its original size as far as 

 it could be traced. 



(7) The stream was deflected by an electrostatic fleld, in which case 

 it was shorter and more scattered than in case of the magnetic deflection, 



(8) Values for the speed of the ion were calculated from the angle 

 of deflection, in magnetic and electrostatic fields, and by placing the two 

 fields in opposition. The average of these was 1.6x10" cm. per second. 



(9) From the kinetic energy of the moving ion and the product of 



Q 



the potential between the points and the charge on the ion values for 



m 

 are calculated, the average value found being 1.8xl0\ 



"A. E. Garrett, B. Sc. — The Pliys. Soc. of 'London Proceedings, Dec. 1909, 

 page 643. 



