24 Sir H. Davy on a [Jan. 



diminished and its base extended : by lowering the pole further, 

 these effects were still further increased, and the undulations 

 were feebler. At a smaller distance the surface of the mercury 

 became plane ; and rotation slowly began round the wire. As 

 the magnet approached, the rotation became more rapid, and 

 when it was about half an inch above the mercury, a great 

 depression of it was observed above the wire, and a vortex, 

 which reached almost to the surface of the wire. 



In the first experiments which I made, the conical elevations 

 or fountains of mercury were about the tenth or twelfth of an 

 inch high, and the vortices apparently as low; but in the expe- 

 riments made at the London Institution, the mercury being 

 much higher above the wire, the elevations and depressions were 

 much more considerable, amounting to the fifth or sixth of an 

 inch. Of course, the rotation took place with either pole of a 

 magnet or either wire, or both together, according to the well- 

 known circumstances which determine these effects. 



To ascertain whether the communication of heat diminishing 

 the specific gravity of the mercury, had any share in these phe- 

 nomena, I placed a delicate thermometer above one of the 

 wires in the mercury, but there was no immediate elevation of 

 temperature ; the heat of the mercury gradually increased, as 

 did that of the wires ; but this increase was similar in every 

 part of the circuit. 1 proved the same thing more distinctly, 

 by making the whole apparatus a thermometer terminating in a 

 fine tube filled with mercury. At the first instant that the mer- 

 cury became electromagnetic, there was no increase of its 

 volume. 



This phenomenon cannot be attributed to common electrical 

 repulsion ; for in the electromagnetic circuit, similar electrified 

 conductors do not repel, but attract each other ; and it is in the 

 case in which conductors in opposite states are brought near each 

 other on surfaces of mercury, that repulsion takes place. 



Nor can the effect be referred to that kind of action which 

 occurs when electricity passes from good into bad conductors, 

 as in the phenomena of points electrified in air, as the follow- 

 ing facts seem to prove. Steel wires were substituted for copper 

 wires, and the appearances were the same in kind, and only less 

 in degree ; without doubt, in consequence of a smaller quantity 

 of electricity passing through the steel wires: and by comparing 

 the conducting powers of equal cylinders of mercury and steel 

 in glass tubes, by ascertaining the quantity of iron filings they 

 attracted, it was found that the conducting powers of mercury 

 were higher than those of steel; the first metal taking up 

 fifty-eight grains of iron filings, and the second only thirty- 

 seven. 



Again ; fused tin was substituted for mercury in a porcelain 

 vessel into which wires of copper and steel were alternately 

 ground and fixed : the elevations were produced as in the mer- 



