EXPERIMENTS WITH lONIZKD AII{. 91 



I do not see how they are to be put under control ' ; inwrely keeping the air ai'ound 

 tlie pliospliorus at constant ten![)erature, etc., is not a sutlicient check on the behavior 

 of the surface itself. 



In sevei-al respects, ueveitlieless, definite advances have been made. It has 

 been shown that the best results can be reached with large splierical condenseis 

 (say 20 centinis., or nioie, in diameter), in which changes of field are produced by 

 a|>plying laigei' potential differences while the ap[)aratus itself is left quite without 

 interference. 



Finally to ascertain in how far the present experiments agree as a whole with 

 the results for plate contlensers, whei'e a theoretically different method is involved, 

 it suffices to compute the value of n^, the numbei' of particles per cubic centim. at 

 one centim. fiom the centei' of the condenser. Since «.j A'in figure 1 2 is of the order 

 of .001 2, oi' referred to natuial logarithms « ^ 7i'=.0028, and since K= /^n e U/C] if we 

 insert J. J. Thomson's value of e = 2.3/10'", and put U of the order of one centim. 

 per second, 6'= 67/10" as above, it follows that n^ — 6.5 X lO'*. Tliis result agrees 

 very well in order with the datum, « „ = 5.5 X 10^ as determined in Chapter IV. from 

 plate condensers by the totally diffei-ent method there [lUi'sued. It also agrees well 

 with the deductions of the last ch:ii)ter (V) obtained by still a different method. 

 Finally if U be put 1.5 cm/sec, the value for ionized air, // ^ =4.3 X 10^, the 

 value deduced by the English philosophers by a totally different process of 

 reasoning. 



' In my recent experiments to be detailed elsewhere (Cf. American Journal Sci., (4), xii, pp. 

 328-346, 1901) considerable progress beyond the status given in the text is in evidence. 



