240 Velocity of the Ions produced in Gases hy Rontgen Rays. 



rated with aqueous vapour, as the results were found to be different 

 in the two cases. This is in agreement with the effect of moisture 

 upon the coefficients of diffusion of the ions, as observed by J. S. 

 Townsend.* A summary of the results obtained is given in the follow- 

 ing table. The results are reduced to a pressure of 76 cm. of mercury, 

 but are not corrected for temperature, the effect of which is not 

 known. 



Ionic Velocities. 



aas. 



Air, dry 



Air, moist 



Oxygen, dry 



Oxygen, moist 



Carbonic acid, dry . . 

 Carbonic acid, moist 



Hydrogen, moist . . . 



Telocity in centi- 

 metres per second 

 in a field of 1 volt 

 per centimetre. 



Yelocity in centi- 

 metres per second 



in a field of Eatio of 

 1 E.S.U. per negative 

 centimetre. to 



positive. 



Tempera- 

 ture. 



Positive. 



ifegative. 



Positive. 



Negative.j 



1-36 

 1-37 

 1-36 

 1-29 

 0-76 

 0-82 

 6-70 

 5-30 



1-87 

 1-51 

 1-80 

 1'52 

 0-81 

 0-75 

 7-95 

 5-60 



408 

 411 

 408 

 387 

 228 

 246 

 2010 

 1590 



1 



561 j 1-375 

 453 1-100 

 540 1-320 

 456 j 1-180 

 243 1-070 

 225 i 0-915 

 2385 i 1-190 

 1680 i 1-050 



13-5° C. 



14 

 17 

 16 



17-5 

 17 



20 

 20 



It is believed that in no case is the error greater than 5 per cent, 

 while most of the observations indicate a considerably greater accu- 

 racy. It is observed that the presence of moisture always diminishes 

 the velocity of the negative ions, and that in carbonic acid the velocity 

 of the positive ions is at the same time markedly increased. The 

 velocity of the negative ions is the greater in all of the cases except 

 for moist carbonic acid. The ratios of the velocities of the ions pre- 

 viously determined for these gases by the writer f were between those 

 given above for the dry and for the moist gases, as the influence of 

 moisture was unknown at that time, and the gases had not been dried. 



E. EutherfordI does not state whether he used dry gases in deter- 

 mining the sum of the velocities of the two ions produced by Eontgen 

 rays ; but his result for air (3*2 cm. per second) agrees with the sum of 

 the values separately obtained above for the two ions in dry air, 

 while his values for oxygen (2 '8 cm. per second) and hydrogen 

 (10'4 cm. per second) correspond to those for the moist gases. His 

 value for carbonic acid (2-15 cm. per second) is higher than those 



* J. S. Townsend, ' PhU. Trans.,' A, vol. 193, 1899. 



t J. Zeieny, • Phil. Mag.,' July, 1898. 



: E. Rutherford, ' Phil. Mag.,' November, 1897. 



