Electro-Magnetic Experiments. 403 



The length of the wire forming the galvanometer may be neglect- 

 ed, as it was only 8 feet long. This result agrees remarkably with 

 the law discovered by Mr. Ritchie and published 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, I of an inch in diameter and wound with about 8 feet of 

 copper wire with a galvanic current from the plates used in Exps. 

 1 and 2 ; the magnetism was scarcely observable in the horse-shoe. 



Exp. 4. The small plates were removed and a battery composed 

 of a piece of zinc plate 4 inches by 7 surrounded with copper, was 

 substituted, when this was attached immediately to the ends of the 8 

 feet of wire wound round the horse-shoe, the v/eight lifted was 4^ lbs.; 

 w^hen the current was passed through the whole length of wire (1060 

 feet) it lifted about half an ounce. 



Exp. 5. The current was passed through half the length of wire 

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



Exp. 6. Tvvo wires of the same length as in the last experiment 

 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. 7. The whole length of the wire was attached to a small 

 trough on Mr. Cruickshank's 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 weight lift- 

 ed in this case was 8 oz., when the intervening Avire 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 appears that 

 the current from a galvanic trough is capable of producing greater 

 magnetic effect on soft iron after traversing more than 3^ of a mile of 

 intervening wire, than when it passes only through the wire surround- 

 ing the magnet. It is possible that the different states of the trough, 

 with respect to dryness, may have exerted some influence on this re- 

 markable result ; but that the effect of a current from a trough, if not 

 increased, is but slightly diminished in passing through a long wire is 

 certain. A number of other experiments would have been made to 

 verify this had not our use of the room been limited, by its being re- 

 quired for public exercises. 



On a little consideration however, the above result does not appear 

 so extraordinary as at the first sight, since a current from a trough 

 possesses more projectile force, to use Prof. Hare's expression, and 

 approximates somewhat in intensity to the electricity from the common 

 machine. May it not also be a fact that the galvanic fluid, in order 

 to produce the greatest magnetic effect, should move with a small ve- 

 locity, and that in passing through one fifth of a mile, its velocity is 

 so retarded as to produce a greater magnetic action? But be this as 



