265 



which takes on more and more the form of an arc as the speed of the 

 machine increases, the air insulation is brob:en down, the air is more 

 highly heated and more highly ionized along the spark path, and a greater 

 number of ions will travel along this narrow path with great speed and due 

 to the outer ones encountering the air molecules, the stream will follow 

 more nearly the curvature of the spark. Farther from the point their 

 speed becomes so small and they become so much scattered, they do not 

 set up a stream so well defined. This same hypothesis applies to the expla- 

 nation of the scattered stream when it was deflected by an electrostatic 

 field. The stfeam retains practically its original diameter past the oppo- 

 site terminal for the magnetic deflection in case of the glow and brush dis- 

 charge, and although scattered may be traced nearly to the opposite point 

 in the spark discharge. In case of the electrostatic deflection, the dis- 

 charge without the transverse field is quite as well defined as those of the 

 magnetic deflected series, while with the transverse electrostatic field the 

 stream is short and not so well defined. If the ions moving with great 

 speed start from the point, and soon by their bombardment start a current 

 of air, at the same time lowering their own speed, they will certainly 

 be scattered, part of them going to the oppositely charged plates, and part 

 to the opposite point. 



If the majority of the negative ions are considered to be ordinary elec- 

 trons and those from the positive point equal in mass to the hydrogen 

 atom, the kinetic energy of the positive ions will be far greater than the 

 negative. They will therefore carry with them a greater current of air. 

 Perhaps it may be permissible to assume that the negative ions are not 

 all single electrons, since it lias been shown by J. J. Thomson* in case 

 of discharge is rarefied gases, that negative ions exist nearly equal in 

 mass to the positive ions, and have the same initial speed. The greater 

 the per cent, of these large ions the greater will be the amount of air 

 set in motion, the greater the velocity of the stream as a whole, and the 

 more defined the stream. If, then, the assumption is made that the stream 

 is produced by the larger ions, it explains the equal deflection of the posi- 

 tive and negative streams in case of the magnetic deflection. 



A few of the photographs show peculiar characteristics. In some 

 there are two streams from the positive point. It was not learned whether 



«J. J. Thomson (Phil. Mag. Ser. 6, Vol. 16, pp. 657-691), 1908; also (Phil. 

 Mag. Ser. 6, Vol. 18, pp. 821-844), 1909. 



