Magnetic Shielding of Concentric Spherical Shells. 95 



difference of potential was shown to be only a volt or two, 

 since a pair of impinging jets ceased to rebound if connected 

 to the opposite terminals of a Grove cell. 



Once more, the effect first observed by Mr. Guitard (1850), 

 and rediscovered by myself and the late J. W. Clark, con- 

 cerning the adhesion of dust-particles or mist-globules in 

 electrified air, is but a more violent variety of the same sort 

 of effect. And the action of electricity on a steam-jet dis- 

 covered by Robert von Helmholtz and afterwards by Shelford 

 Bidwell, and worked at by Richarz, Aitken, J. J. Thomson, 

 and others, may not be very different. 



Thinking of the Lord Rayleigh variety of experiment as 

 in many respects the most definite ; it is natural to explain it 

 electrolytically as due to the polarisation of the water-drops, 

 or the formation in each drop of molecular chains each with 

 a negatively charged oxygen atom at its termination on one 

 hemisphere and a positively charged hydrogen atom at its 

 opposite extremity. 



Such drops then colliding about the region of their poles 

 would be attracted not only by their ordinary cohesive forces, 

 but by electrical force also, and thus the effective molecular 

 range would be increased and cohesion might set in over an 

 unusual distance. 



In some such way I have allowed myself to fancy that the 

 adhesion of my knobs might be explained, and I suggest that 

 the conductivity of a chain of metallic filings under an electric 

 polarising influence may be due to something of the same 

 cause. 



That a tap should break the minute points of contact is 

 likely enough, though I see no reason why another tap should 

 restore communication, — if so it does. 



At the last moment I write this and send it off in the 

 hope that it may arrive in time to be read at the Meeting 

 as a contribution to the discussion on these interesting 

 experiments. 



Nov. 23, 1893. 



VII. On the Magnetic Shielding of Concentric Spherical Shells. 

 By A. W. Ruckek, F.R.S.* 



SPECIAL interest has of late attached to the problem of 

 shielding magnetic forces by means of iron screens, and 

 recently the Astronomer Royal has described the arrange- 

 ment (designed by Messrs. Johnson and Phillips) by which 

 * Communicated by the Physical Society : read November 24, 1893. 



