( 428 ) 
*=*-»'(?<*)+ 1) = 
then follows out of it for g (x) 
«* + g 
r* + «' 
where a, b, c and d must satisfy 
ad — be cd d * c s 
« + ff 20^ —2y‘ 
In this case too the form (c?') of (a?) can be determined without 
any difficulty. 
The necessity of this supplement did not become quite clear to 
me until I received a communication of Dr. L. E. J. Brouwer, who 
was so kind as to draw my attention to this lack and who likewise 
brought out the immediate connection between the standardform ( D) 
and that of Schroeder. I set great store by the fact of thanking him 
kindly for his observations. 
Physics. “Remarks on the Experiments of Wilson and Martyn 
on the Velocity of Rotation of the Electric Discharge in Gases 
in a Radial Magnetic Field” By Dr. J. A. Vollgraff. (Com¬ 
municated by Prof H. A. Lorentz). 
(Communicated in the meeting of October 80, 1909). 
Wilson and Martyn *) have proposed a theory on the rotation of 
the electric discharge in gases at low pressures in a radial magnetic 
field, agreeing satisfactorily with their experiments. The discharge 
consists in a motion of positive and negative ions. 
They find for the value of the velocity of rotation 
U=k l k 2 HX ,.(1) 
H being the magnetic and X the electric intensity at the place of 
the discharge, and k x and k t the velocities which unit electric inten¬ 
sity acting on the gas gives to a positive and a negative ion resp- 
The apparatus was composed of two vertical coaxial cylinders of 
glass Cj and C, along the axis of which an electromagnet was so 
placed that one of its poles was situated in the middle of the magnet 
and at the same time in the middle of the axis. The magnetic field 
b H. A. Wilson and G. H. Martyn. “On the Velocity of Rotation of the Electric 
Discharge in Gases at Low Pressures in a Radial Magnetic Field”. {Proc. Jty- 
Soc. Ser, A. Vol. 79, N° A 532, 2 Aug, 1907), 
