Electromagnetic Effect of Convection-Currents. 457 



nearly up to the surftice of the disk and taken with all the 

 brass work must form a condenser of a certain capacity with 

 the inner face of the gold foil. 



This made a change necessary in the method of working ; 

 the disks had to be earthed and the glasses charged. This 

 was done ; but no\v the deflexions were found always to be 

 greater with positive rotation (Zenith, North, Nadir, South) 

 then with negative. 



It was considered possible that the brushes might have 

 something to do with this, so they were taken off. Earth 

 connexion with the disk was made by drilling through to the 

 surface of the disk in the line of the axle and setting in a 

 screw, which came flush with the surface and also made con- 

 tact with the axle; this, however, made no difference, the 

 deflexions for negative rotation were always smaller. 



Table I. gives the results of a number of observations. 

 All were taken with the plates charged and the disks earthed 

 by means of the axle. 



The meaning of the letters has been given ; l/y8 is directly 

 proportioned to the needle sensitiveness. 



Table I. 



No. 



Eotation. 



X. 



e. 



N. 



(7. 



1//3. 



2A. 



V. 













mm. 





1 



+ 



2-54 



1-24 



122 



1-16 



1-50. 10' 



5-3 



2-42.10" 



2 



+ 



2 57 



„ 



125 



1-30 



311 



90 



3-38 



3 



+ 



« 



„ 



129 



1-23 



2-15 



6-94 



300 



4 



— 





„ 



129 



1-23 



jj 



5-58 



3-68 



5 



+ 



>> 



1-21 



127 



1-21 



2-25 



5-6 



3-74 



6 



— 





1^ 



133 



1-21 



,, 



5-7 



3-74 



7 



+ 



» 



)) 



130 



1-47 



J, 



8-4 



3-10 



8 



_ 







133 



1-47 



,, 



7-3 



3-64 



9 



+ 



,j 



1-24 



121 



1-32 



2-22 



9-4 



2-26 



10 





,, 



,j 



130 



1-32 



jj 



7-2 



316 



11 



+ 



}f 



J, 



125 



1-26 



217 



7-6 



2-70 



12 







,j 



12r5 



1-26 



J, 



5-7 



3-64 



13 



+ 



2-85 



1-50 



125 



1-19 



223 



6-5 



2-82 



14 



— 



M 



9J 



129 



1-19 



j^ 



5 



3-78 



15 



— 







125 



1-11 



219 



5-85 



2-82 



16 



+ 



M 



1-43 



127 



1-08 



2-35 



73 



2-46 



17 





)> 



5) 



128 



1-08 



,, 



5-4 



3-32 



18 



— 







129 



108 



, 



5-3 



3-42 



19 



+ 



3-22 



1-80 



123 



113 



2-44 



5-1 



3-30 



20 





» 



" 



124 



1-13 



" 



4-9 



3-48 



3-19x1010 



The sudden variations in the values of 1//3 are due to 

 changes purposely made in the needle. 



