34 Dr. H. Pender on the Magnetic 



We succeeded in reaching tins degree of accuracy by using 

 the following precautions : — 



1. Using two comparison condensers whose capacities Cx 

 and C 2 differ as little as possible from each other. 



2. Covering all the portions of apparatus employed to 

 produce high-frequency currents (Ruhmkorff-coil, spark- 

 gap, &c.) with a metallic cage, in order to avoid electrostatic 

 actions between those latter and the various branches of the 

 Nernst bridge. 



3. Covering with a metallic cage also the two comparison 

 condensers. 



4. Avoiding the use of any conductors in the neighbourhood 

 of the wires, and especially of the spirals. 



By this method the following values for the self-induction 

 of our circuits have been obtained : — 



Circuit. Self-induction. 



Spiral No. 1 29470 



„ No. 2 74140 



., No. 3 17460 



Wire No. 4 3669 



In these values the self-induction of tubes and copper 

 strips establishing the connexions are also included. 



II. On the Magnetic Effect of Electrical Convection. — II. 

 By Harold Pender, Ph.D.* 



~~ O INCE the publication of the results of his first experi- 

 O ments on the magnetic effect of a moving charged 

 bodv t? the author has continued his investigations, with re- 

 sults in every way confirmatory of those of the previous 

 experiments. A brief account of these later experiments 

 may not be without interest, as they were performed under 

 entirely new and more favourable conditions, and gave 

 results which are far more consistent than those previously 

 obtained. 



M. OremieuJ, in criticizing the previous paper of the 

 author, suggested that the agreement between the observed 

 and calculated values of the magnetic effect of the moving- 

 charged disks was due to the fact that the speeds and potential 

 of the disks were of such critical values that a slight leak in 

 the insulation would produce the observed effect. The first 

 step then was to test this criticism by varying the speeds and 



* Communicated bv Prof. J. S. Ames. 



f Phil. Mag. ii. p. 169 (1901) ; Phys. Ptev. xiii. p. 203 (1901). 



\ Journ. de Phys., Dec. 1901. 



