TH E 

 L ^N, EDINBURGH, and DUBLIN 



PHILOSOPHICAL MAGAZINE 



AND 



JOUIINAL OF SCIENCE. 



[FIFTH SERIES.] 



JUNE 1889. 



LII. On the Electromagnetic Effect of Convection- Currents. 

 By Prof. Heney a. Rowland, and Gary T. Hutchinson, 

 Fellow in Physics, Johns Hopkins University *. 



[Plate IX.] 



THE first to mention the probable existence of an effect of 

 this kind was Faraday tj who says : — " If a ball be elec- 

 trified positively in the middle of a room and then be moved 

 in any direction, effects will be produced as if a current in 

 the same direction had existed." He was led to this cpnclu^ 

 sion by reasoning from the lines of force. 



Maxwell, writing presumably in 1872 or 1873, outlines an 

 experiment, similar to the one now used, for the proof of this 

 effect. 



The possibility of the magnetic action of convection-currents 

 occurred to Professor Rowland in 1868, and is recorded in a 

 note-book of that date. 



In his first experiments, made in Berlin in 1876, Prof. 

 Rowland used a horizontal hard rubber disk, coated on both 

 sides with gold, and revolving between two glass condenser- 

 plates. Each coating of the disk formed a condenser with 

 the side of the glass nearer it ; the two sides of the disk were 

 charged to the same potential. The needle was placed per- 

 pendicular to a radius, above the upper condenser-plate, and 

 nearly over the edge of the disk. The diameter of the hard 

 rubber disk was 21 centim., and the speed 61 per second. 



* Communicated by the Authors. 



t Experimental Researches, yol. i. art. 1644. 



Phil. Mag. S. 5. Vol. 27. No. 169. June 1889. 2 H 



