1877.] 



Induction in Liquids and Gases. 



41 



liquid was used as a secondary circuit. He coiled round the armature of 

 an electromagnet an india-rubber tube filled with dilute sulphuric acid, 

 and found, on making and breaking the primary circuit, the induced cur- 

 rents generated in it, as in the case of metallic conductors ; but he could 

 not obtain any effect when brine, sulphuric acid, or other solutions were 

 rotated in basins over a magnet, or enclosed in tubes and passed between 

 the poles. He failed also to detect any magneto-electric current in water 

 flowing across the earth's lines of magnetic force (viz. in the river 

 Thames). 



Since the reason for these negative results is not at once obvious, it 

 seemed desirable to repeat and extend them to other cases, so that, if 

 possible, the analogy of electrolytic with solid conductors might, in 

 respect to magneto-electric induction, be completed. In addition, the 

 subject involves the interesting question of the magneto-electric pheno- 

 mena accompanying the flow of ocean-currents and other large masses 

 of water. 



Three cases of induction in liquids flowing in a magnetic field or tra- 

 versed by lines of magnetic force have been examined. 



1. Production of induced current in a liquid stream flowing uniformly 

 in a constant magnetic field. — When a stream of conducting fluid flows 

 vertically down between the poles of a magnet a transverse current is 

 produced in a direction at right angles to the lines of force and line of 

 flow. This was obtained in the following way : — A glass tube, about 200 

 centims. long and 2 centims. wide, had platinum plates 15 millims. wide 

 placed along its inside and at opposite sides, with their lengths parallel to 

 the axis of the tube. Platinum wires welded to these plates were sealed 

 through the glass. The plates were curved to lie closely against the sides 

 of the tube. This tube was placed vertically between the poles of a large 

 electromagnet, the line joining the platinum plates being at right angles 

 to the line of the poles. 



To the upper end of the tube was attached another, leading to a reser- 

 voir of dilute sulphuric acid placed high above the floor ; to the lower 

 end a tube leading to a receptacle on the floor. The platinum plates 

 were then connected with a distant galvanometer. When the magnet 

 was not excited, no flowing of the liquid had any effect on the galvano- 

 meter; but when it was excited, at the moment the flow began the 

 galvanometer showed a deflection of 10° to 15°. Since the only part of 

 the galvanometer circuit in motion is the liquid, this deflection was due 

 to the magneto-electric current generated in it by its movement. It was 

 noticed that the plates were polarized by the currents so created. As a 

 consequence of this, the deflection of the needle soon fell to zero ; and 

 on the liquid flow being stopped, a polarization current in the opposite 

 direction was obtained. This proved that in experiments on induction in 

 liquids, in order to obtain any constant current, non-polarizable electrodes 

 must be used. 



