﻿124 Mr. Clinton J. Dayisson on the Positive 



its upper surface the salt to be examined, and is electrically 

 heated. D designates a slit in the plate BB. 1) is parallel 

 to C and approximately equal to it in width. Behind D 

 is another plate, E, parallel to BB and insulated from it. 

 BB and E are joined rigidly together. BB is free to move 

 in its own plane perpendicularly to the length of D. 



The parts of the apparatus to the left of the dotted line FF 

 are in vacuo, but connect electrically and mechanically with 

 the parrs in air as indicated. AA and C connect to a battery 

 of accumulators, G, which maintains them at a positive 

 potential relative to the earth. BB and E are connected, as 

 shown, to a system of mercury-cup switches. 



If, now, positive ions are being emitted by the strip C, or 

 by a substance on its upper surface, these will be carried 

 across the space between AA and BB by virtue of the electric 

 field. Most of these will reach BB, and will carry charge 

 to it at a uniform rate, constituting a current to which we 

 will refer as the current?!. A part of the ions will, however, 

 pass through D and carry charge to E. The number of 

 coulombs reaching E per second will be referred to as the 

 current i 2 . The ratio of i 2 to (?'i + i 2 ) will depend upon the 

 position of the slit D. From the symmetry of the apparatus 

 it is clear that this ratio will be a maximum when D is 

 opposite the strip. If, however, a magnetic field is estab- 

 lished parallel to the strip in the space between AA and BB 

 the symmetry will be destroyed ; we should expect to find 

 the maximum in i 2 j(i\-\ h) displaced in a direction depending 

 upon the direction of the magnetic field and by an amount 

 depending upon nearly every physical quantity involved, 

 including the value of e/m for the ions. The way in which 

 these physical quantities are related will be considered later. 

 For the present we consider the method of determining 



Referring again to the system of mercury-cup switches 

 shown in fig. 1, it will be seen that when R and T are in 

 place the currents t } and i 2 will be shunted directly to earth. 

 If T is removed the current i x will charge up the insulated 

 system including BB, the condenser M, and the wires joining 

 them, while the current i 2 will charge up the system in- 

 cluding the plate E, the electrometer N, and their connecting 

 wires. If, after these currents have been passing for a 

 convenient time, say t seconds, the connexion R is removed, 

 the parts of the two systems to the right of this connexion 

 will have acquired potentials which will depend upon the 

 total charges received by the two systems. These potentials 

 will not he exactly proportional to the charges respectively, 



