266 Prof. Faraday on Electro-dynamic Induction in Liquids. 



formed conductors between the fluid helix and the galvanometer : 

 the whole was attached to a wooden frame so as to protect the 

 helix from pressure or derangement when moved to and fro. 

 The quantity of fluid contained in the helix was about 3 cubic 

 inches in the length of 7 feet. The galvanometer was of copper 

 wire, ^'yth of an inch in diameter and 164 feet in length, occu- 

 pying 310 convolutions; it was 18 feet from the magnet, and 

 connected with the helix by thick wii-es dipping into cups of 

 mercury. It was in the same horizontal plane with the magnetic 

 poles, and very little aff"ected by direct action from the latter. 



A solution formed by mixing one volume of strong sulphuric acid 

 and three of water was introduced into the helix tube, the iron 

 keeper placed on the helix, and the whole adjusted on the magnetic 

 poles in such a position, that the ends of the copper connectors in 

 the tube were above the iron cylinder or keeper, and were advanced 

 so far over it as to reach the perpendicular plane passing through 

 its axis : in this position the lines of magnetic force had no ten- 

 dency to excite an induced current through the metallic parts of 

 the communication. The outer ends of the copper terminals 

 were well connected together and the whole left for a time, so 

 that any voltaic tendency due to the contact of the acid and 

 copper might be diminished or exhausted : after that, the copper 

 ends were separated, and the connexions with the galvanometer 

 so adjusted, tliat they could be in an instant either interrupted, 

 or completed, or crossed at the mercury cups. Being interrupted, 

 the magnet was excited by the full force of the battery, and then 

 the direct magnetic efiect on the galvanometer was observed : 

 the helix had been so arranged that any current induced in it 

 should give a deflection in the contrary direction to that thus 

 caused directly by the magnet, that the two efiects might be the 

 better separated. The battery was then disconnected, and when 

 the reverse action was over, the galvanometer connexions were 

 completed with the helix ; this caused a deflection of only 3°, 

 due to a voltaic current generated by the action of the acid in 

 the helix on the copper ends : it showed that the connexion 

 throughout was good; and being constant in power, caused a 

 steady deflection, and was thus easily distinguished from the final 

 result. Lastly, the battery Avas thrown into action upon the mag- 

 net, and immediately the galvanometer was deflected in one direc- 

 tion, and upon breaking battery contact it was deflected in the 

 other dh'cction, so that by a few alternations considerable swing 

 could be imparted to the needles. They moved also in that par- 

 ticular manner often observed with induced currents, as if urged 

 by an impact or push at the moment when the magnet was 

 excited or lowered in force ; and the motion was in the revei'se 

 direction to that produced by the mere direct action of the mag- 



