Effect of Electrical Convection, 



directly. We have the formula 



D 



201 



A= 



S(Ji" 



The current i was obtained from an ordinary commercial cell 

 in series with several thousand ohms. The E.M.F. of this 

 cell was determined by comparison with a standard Clark cell. 

 The total resistance of the circuit w T as measured by a standard 

 bridge. The internal resistance of the battery was less than 

 an ohm. In some determinations a Daniell cell was used in 

 place of the commercial cell. Table II. gives a series of 

 determinations of A, for various values of the quantities 

 involved, i is given in c.G.s. electromagnetic units. The 

 value of A is seen to be constant within the limits of error of 

 observation. After using the commutator for these determi- 

 nations it was always necessary to thoroughly clean the 

 reverser with emery-cloth and to reset the brushes, before it 

 could again be used to reverse the charge on the disks. 







Table II. 





s. 



2D. 



C. 



i. 



A. 



153 



158 



7-46 



•628 xiCT 4 



•1101x10* 



205 



107 



734 



•317 



1122 



197 



200 



147 



•317 



•1089 



372 



176 



142 



•317 



•1136 



177 



158 



12-8 



•317 



•1100 



171 



318 



134 



•632 



•1098 



214 



245 



168 



•314 



•1085 



86-7 



88-2 



165 



•276 



•1117 



160 



198 



203 



•276 



•1105 



215 



217 



168 



•276 



•1089 







Mean 



... -1104 



The quantities to be measured in conjunction with the 

 deflexion due to the rapid reversal of the charge on the 

 rotating disks are the following : — 



(1) The number of reversals per second. This was deter- 

 mined by a velocimeter attached to the shaft of the commu- 

 tator. The time required for 200 revolutions was determined 

 by a stop-watch. One turn of the shaft corresponds to four 

 reversals. 



(2) The speeds of the two disks. The time required for 

 20 complete turns of each of the speed-counters was deter- 

 mined by a stop-watch. Each counter has 199 teeth, so that 



