660 Dr. A. S. Eve on the Effect of 



any special precautions, so that doubtless there was much 

 dust in the air. 



Taking the ionic charge to be 4'6xl0- 10 , and assuming 

 that there were no multiple-charged ions present, then the 

 number of ions detected in the testing vessel of the Ebert 

 instrument for various distances of the radium were as 

 follows : — 



Series. n+ • n— Katio. 



1 51000 46500 M0 



2 .... 27000 13700 (1*97) 



3 30200 22800 1-33 



4 18000 16000 1-12 



5 9900 7850 1*26 



Mean 1-20 



Without radium... 1740 



1420 



1*23 



Thus, with a wide variation of conditions there appears to 

 be an excess of positive over negative ions equal to about 

 20 per cent., whereas we know that equal quantities of 

 positive and negative electricity must have been produced 

 under all conditions by the ionization. Moreover, when an 

 earthed, wide-meshed gauze cylinder was placed in the cone 

 and over the testing vessel so as to increase the loss by 

 diffusion, the number of ions of each charge was certainly 

 diminished considerably, but the ratio n + /n— was not much 

 altered. Hence the inequality was not due to diffusion 

 alone. 



This deduction then appears inevitable, that more negative 

 than positive ions rapidly become either attached to dust or 

 otherwise transformed into large ions, and pass without 

 detection through the testing vessel of the Ebert apparatus. 



It might, be expected that, because the small negative ion 

 is more mobile than the small positive ion, an excess of the 

 negative would be shown by the electroscope. But it is not 

 so, because ad small ions are stopped in the testing vessel, 

 and previous to the arrival there of the air examined there 

 has been a greater loss of negative than positive small ions 

 in virtue of the greater mobility of the former. And this 

 loss has taken place in two or three ways : by diffusion to 

 parts of the apparatus employed ; by diffusion to centres such 

 as dust, mist, and smoke in the air : and, as Pollock has 

 shown, by the apparent loading due to water vapour, even 

 when far from saturation. The fact that these three operations 

 act in the same direction, all causing an excess of small 



