Determination of e, N, and Related Constants. 7 



between the results of Professor Ehrenhaft and his pupils 

 and those obtained at the Ryerson Laboratory has been 

 reported in detail elsewhere *. It is sufficient here to say 

 that, although we have worked extensively with droplets 

 of substances other than oil, particularly with mercury, 

 upon which the irregularities are chiefly found in the 

 Vienna work, and with particles of the same order of 

 magnitude as those there used, we have found no indi- 

 cations whatever that the method, when properly used, even 

 remotely suggests the existence of charges which are not 

 equal to or multiples of the electron. We have studied, 

 thousands of drops of many different substances in a 

 number of different gases, and have never found one whose' 

 charge did not fit into an arithmetic series whose greatest 

 common divisor was the electron. We have definitely dis- 

 proved Ehrenhaft's contention that this greatest common 

 divisor is a function of the radius of the drop. Further 

 evidence of this independence is given herewith. We have 

 also discovered what seem to us wholly adequate reasons for 

 the irregularities observed by Professor Ehrenhaft. 



5. The Precision of the Method, 



The consistency of the results on different drops is 

 sufficient guarantee of the precision of the method, pro- 

 vided no constant error inheres in the measurement of the 

 dimensions of the condenser, the volts, the time, or the 

 viscosity of air, and provided the speed with which a given, 

 drop moves through the gas is strictly proportioned to the 

 force acting upon it, as it is assumed to be. This last 

 point was very carefully studied in the 1912 work, andi 

 considerable time has been given to studying it again. 

 Incidentally, since for convenience most of the preceding 

 work was done on drops charged with electrons of one 

 sign only, and since it was thought conceivable that the 

 electron of opposite sign might have a slightly different 

 value and thus account for the discrepancies between dif- 

 ferent methods of getting e, exact demonstration has here 

 been made that the sign of the charge is wholly immaterial. 

 This means simply that an nn-ionized gaseous molecule 

 possesses no residual charge of either sign which is at all 

 comparable with the electron. Some evidence upon these 

 points is contained in Table I. (p. 8), which records experi- 

 ments in which a given drop was alternately loaded with 

 positive and negative electrons. It will be seen, not only that 



* Phys. Rev. Dec. 1916, "The Existence of a Subelectron ? " 



