the Motion of Electrons in Gases. 879 



electric force to the pressure. With the ranges of forces 

 and pressures used in these experiments the ahove condition 

 is satisfied by the values of W and k obtained with nitrogen 

 and hydrogen, as had previously been obtained with air. 

 The results of the principal determinations are given in 

 Tables I. and II., which are arranged in groups, each group 

 corresponding approximately to one value of the ratio Zjp. 

 It will be seen that both W and k remain practically 

 constant when the pressure and the force are reduced in the 

 same proportion. 



For certain forces and pressures the apparatus was not 

 adapted for finding the velocities, so that there are some 

 blank spaces in the column under W. For example, with a 

 pressure of 20 millimetres and a force of 33*4 volts per 

 centimetre in nitrogen, the magnetic force required to pro- 

 duce the deflexion of the stream necessary for measuring 

 the velocity could only have been obtained by a current of 

 more than 20 amperes which would have injured the coils. 

 Also with the smaller electric forces the lateral divergence 

 of the stream was, in some cases, so large that some of the 

 stream was deflected on to the earth ring C 4 by the magnetic 

 field, which would have introduced an error in the deter- 

 mination of the velocity W. 



With the large values of Zjp electrons are generated in 

 the stream by collisions of electrons with molecules. This 

 effect does not introduce any error in the measurements of 

 k or W since this process of ionization increases by the same 

 proportion the number of electrons in all parts of the stream. 



8. Velocities W in direction of electric forces Z, and 

 factors k by which energy of agitation of electrons exceed 

 the normal value corresponding to 15° C, in nitrogen, 

 hydrogen, and oxygen are given in the following tables. 



9. In oxygen different values were obtained for W and k 

 in the cases where the ratio Zjp was the same, especially 

 when p was taken over ranges including large pressures, 

 but with the smaller pressures and larger values of Zjp the 

 discrepancies were not great. 



Examples of determinations oE the velocities W and the 

 quantities k with electrons moving in oxygen are given in 

 Table HI., which show that both W and k tend to increase 

 when Z and p are reduced in the same proportion. 



This effect would occur if the electrons tended to become 

 permanently associated with molecules or other small par- 

 ticles as they moved through the gas. Thus if electrons 

 moved under a force Z and pressure /> and a certain number 



