Erskine. — On Magnetic Screening. 



181 



A second set of experiments was made with four leyden- 

 jars, arranged in parallel, placed in the circuit, and the needle 

 placed in direction b. The length of the needle used in this 

 set of experiments was 74-5mm. The observations are here 

 tabulated : — 



The results of this set of experiments were that the silver 

 was equivalent to 8-5 layers of tinfoil, the copper to 9-3 layers, 

 the zinc to 9 layers, and the lead to 6-1 layers. 



These experiments show that the thicknesses of dilierent 

 metals required to produce the same screening are proportional 

 to the specific resistances of the metals. 



Ill the next table the equivalent thicknesses obtained by 

 experiment are compared with those calculated by taking the 

 thickness proportional to the specific resistance : — 



Professor J. J. Thomson, in a paper on " The Eesistance 

 of Electrolytes to the Passage of very Eapidly- alternating 



