1831] WRITINGS OF JOSEPH HENRY. 41 



The length of the wire forming the galvanometer may be 

 neglected, as it was only 8 feet long. This result agrees re- 

 markably with the law discovered by Mr. Ritchie and pub- 

 lished in the last No. of the Journal of the Royal Institution 

 of Great Britain. 



Exp. 3. The galvanometer was now removed, and the 

 whole length of the wire attached to the ends of the wire of 

 a small soft iron horse-shoe, ^ of an inch in diameter, and 

 wound with about 8 feet of copper wire with a galvanic cur- 

 rent from the plates used in Experiments 1 and 2 ; the mag- 

 netism was scarcely observable in the horse-shoe. 



Exp. 4. The small plates were removed and a battery com- 

 posed of a piece of zinc plate 4 inches by 7 inches surrounded 

 with copper, was substituted ; when this was attached imme- 

 diately to the ends of the 8 feet of wire wound round the 

 horse-shoe, the weight lifted was 4| lbs. : when the current 

 was passed through the whole length of wire (1060 feet) it 

 lifted about half an ounce. 



E.vp. 5. The current was passed through half the length 

 of wire (550 feet) with the same battery, it then lifted 2 oz. 



Exp. 6. Two wires of the same length as in the last ex- 

 periment were used, so as to form two strands from the zinc 

 and copper of the battery : in this case the weight lifted was 

 4 oz. 



Exp. 1. The whole length of the wire was attached to a 

 small trough on Mr. Cruickshanks' plan, containing 25 

 double plates, and presenting exactly the same extent of 

 zinc surface to the action of the acid as the battery used in 

 the last experiment. The w^eight lifted in this case was 8 

 oz. ; when the intervening ■wire was removed and the trough 

 attached directly to the ends of the wire surrounding the 

 horse-shoe it lifted only 7 oz. From this experiment, it ap- 

 pears that the current from the galvanic trough is capable 

 of producing greater magnetic effect on soft iron after trav- 

 ersing more than | of a mile of intervening wire, than 

 when it passes only through the wire surrounding the mag- 

 net. It is possible that the different states of the trough, 

 with respect to dryness, may have exerted some influence 



