Question of Valency in Gaseous Ionization. 759 



working speeds recur. After all the possible speeds have 

 been located it is only necessary to see whether one of them 

 is ever skipped in the capture of a new ion, in order to know 

 whether or not that ion was a double. Table I. represents 

 the results of experiments made with very hard X rays pro- 

 duced by means of a powerful 12-inch Scheidel coil, a 

 mercury-jet interrupter, and a Scheidel tube whose equivalent 

 spark-length was about 5 inches. The radius a of the drop 

 is computed, as explained in previous papers, from the modified 

 form of Stokes's law 



9 fju \ a/' 



The absolute values of the charges carried by the drops 

 have been computed as in the preceding papers and agree 

 in every case, within the limits of observational error (4 or 

 5 per cent.), with the value of E previously found, viz. 

 4*891 x 10 -10 . However, no attempt has been made in these 

 experiments to make precise determinations of speed since a 

 high degree of accuracy of measurement was not necessary 

 for the purpose for which the investigation was undertaken. 

 We are here only concerned with the relative values of the 

 charges carried by a given drop after the capture of one or 

 more ions from the air. These relative values could be 

 determined, if desirable, with a very high degree of accuracy. 

 For the equation 



shows that for a given drop the charge is proportional simply 

 to [Vi + v^j. Furthermore, these relative values are quite 

 independent of errors due to convection currents, or other 

 constant disturbing forces ; for Vi is simply the velocity 

 under the joint action of all the outside forces before the 

 field is thrown on, and v 2 is the velocity under the action of 

 all these forces plus that of the field. Whatever then the 

 size of the drop it is only necessary, for our present purpose, 

 to determine the greatest common divisor of all the observed 

 values of v 1 + v 2 . The number of elementary charges upon 

 the drop is then the value of [v l + v 2 ) under consideration 

 divided by this greatest common divisor. With most of the 

 drops actually worked with this greatest common divisor was 

 one of the observed values of (vi + v 2 ), so that the differences 

 were so great that no high degree of accuracy was necessary 

 in order to be very certain of each number of the multiple 



* Loe. cit. 



