492 Study of Franklin s Experiment on Ley den Jar. 



rubber gloves, one can manipulate inside without introducing 

 moisture. 



The Franklin experiment with, glass dielectric was then 

 repeated with the dried glass in a thoroughly dried atmo- 

 sphere. 



The effects observed were now no longer the same as> 

 before, but were the same as described with the paraffin jar. 

 Thar, is, after charging and taking out the inner coating and 

 touching it to the outer coating and replacing, there was 

 only a slight charge remaining, due doubtless to absorption. 

 For all practical purposes the characteristic actions as de- 

 scribed in the text-books were wanting, and the results come 

 in line with the Faraday-Maxwell theory. 



It is clear from other experiments I have made (see Physical 

 Society's Proceedings, 1912) that, in the case of the glass 

 jar, condensed moisture on its surface is under all ordinary 

 circumstances sufficient to form a semi-conducting film, of 

 high resistance, but sufficiently conducting for the charge 

 on the electrodes to escape to it when one is removed, or 

 before, especially as when the experiment is tried under 

 conditions as above, the electroscope shows that if the 

 electrodes are separated the same action takes place as when 

 the cover is removed from an electrophorus, that is as the 

 electrodes are separated their difference of potential rapidly 

 increases. 



This is more the case as the dielectric constant of glass is 

 so high that the slope of the potential is chiefly concentrated 

 on and is very great across any small air space between the 

 glass and the electrodes. 



A small motion of the electrodes already charged to a 

 fairly high potential, therefore, raises this potential at least 

 two or three times so that there is a strong tendency for the 

 charge to flow to the glass surface, even if there is only 

 momentary contact at two or three points. 



I have related my work on this experiment at some length 

 because it became more and more clear to me that to arrive 

 at any clear understanding of the actions of electric fields 

 on dielectrics, the correct interpretation of the experiments 

 is essential. 



It has always appeared to me that this experiment was 

 about the most striking and most fundamental in all the 

 realm of electrostatics. It seemed so convincing that for 

 many years I, and I know numbers of others, have accepted 

 it and still do without question, as ordinarily interpreted. 



It is such a striking experiment that when I began to 

 doubt its interpretation it appeared to me that to leave it 

 without rational explanation left a fundamental point in 



