IONS PEODUCED BY RONTGEN RAYS IN GASES AND VAPOURS. 261 



will be noticed that, although the actual temperatures are given, no correction has 

 been made, as such correction would almost certainly lie within the limits of error of 

 the experiment. 



The figures in the second column give the electric field X in volts per centimetre. 

 The third and fourth columns give the height in centimetres from the bottom of the 

 falling weight W to the movable contact K', when the latter is in the positions 

 corresponding respectively to the first and second nicks in the typical curve (vide 

 fig. 3, which was obtained in the measurement of a negative mobility). The fifth 

 column contains the equivalent time interval / expressed as the fraction of a second ; 

 it was calculated by means of the ordinary formula for a body falling freely under 

 gravity. The values in centimetres per second of the mobility k are calculated from 

 the equation k = 1/X^, and, corresponding to the stated pressure, are given in the 

 seventh column. In the eighth and ninth columns are given the mobilities corre- 

 sponding to a potential gradient of 1 volt per centimetre and to a pressure of 760 mm. 

 of mercury ; these values are based on the assumption that the ionic velocity is 

 proportional to the field intensity and is inversely proportional to the pressure. 



An asterisk affixed to a mobility value denotes that this value was not included in 

 estimating the mean ; these values showed marked deviations from the law 

 pk = constant, the reasons for these deviations in some cases not being apparent, but 

 in most cases being due to the pressures lying outside the range for which the law is 

 applicable. 



rr, TTI i Height of fall to 



Tern- Electric ___ T . p ; 



perature. field. lgt ^.^ 2nd point + 



C. volts/cm. cm. cm. sec. mm. om./sec. cm. /sec. cm. /sec. 



Am. 

 14 38-7 54-8 50-0 0-0150 758 1'72 1'7 



16-5 



49-5 0-0166 762 1-56 1-56 



1-82 



1-85 



15-5 50-7 0-0127 264 5'08 1-76 



50-0 0-0150 264 4-30 1'49 



5-8 51-0 0-0118 98 14-61 1'88* 



, , , , [' positive ion 1 54 cm./sec. 



Mean values of *-, { egative >f j.yg / ( 



