406 Electro-magnetic Experiments. 



Exp. 17. With 6 wires, each 30 feet long, attached to the galvanic 

 element ; the weight lifted was 375 lbs. 



Exp. 18. The same wires used in the last experiment, were united 

 so as to form 3 coils of 60 feet each ; the weight supported was 290 

 lbs. This result agrees nearly with that of Exp. 11, though the same 

 individual v/ires were not used ; from this it appears, that 6 short 

 wires are more powerful than 3 of double the length. 



Exp. 19. The wires used in Exp. 10, but united so as to form a 

 single coil of 120 feet of wire, lifted 60 lbs,, in Exp. 10, the weight 

 lifted was 200 lbs., this is a confirmation of the result in the last ex- 

 iperiment. 



Exp. 20. The same wires used in the last Exp., were attached to a 

 small compound battery, consisting of 2 plates of zinc and 2 of cop- 

 per, after the plan of Prof. Hare, and containing exactly the same 

 quantity of zinc surface, as the element in the last Exp., in this case 

 the weight lifted was 110 lbs., or nearly double of that in the last. 

 This result is in strict accordance with that of Exp. 7, the two plates 

 having more projectile force, and thus produce a greater effect with a 

 long wire. 



In these experiments a fact was observed, which appears somewhat 

 surprizing, when tlie large battery was attached and the armature 

 touching both poles of the magnet, it was capable of supporting more 

 than 700 lbs. but when only one pole is in contact it did not support 

 more than 5 or 6 lbs., and in this case we never succeeded in making it 

 lift the armature (weighing 7 lbs.). This fact may perhaps be com- 

 mon to all large magnets, but we have never seen the circumstance 

 noticed of so great a dijfFerence between a single pole and both. 



A number of experiments were also made with reference to the 

 best form of the iron to receive magnetism, but no very satisfactory 

 results were obtained ; of these however, the following are considered 

 as not uninteresting, 



Exp. 21. A cylindrical bar of iron weighing 13 oz. 4^ drachms, 

 and bent into a horse-shoe, was covered with 2 coils of wire each 60 

 feet long; with the small battery used in the last Exp., it lifted 42 lbs. 



Exp. 22. A rectangular flat bar if of an inch wide, and i of an 

 inch thick, also bent into a horse-shoe, Aveighing 9 oz. 3 dr., and of 

 exactly the same surface as the bar used in the last Exp., lifted, with 

 the same wires and battery, 35 lbs. 



Exp. 23. A piece of a gun barrel, little less than an inch in diame- 

 ter and about 8 inches long, and from -^-^ to Jj of an inch thick, 

 weighing 8 oz. 3f dr. with the wires and battery as before, lifted 40 lbs. 



From the last Exp., it appears that a given quantity of iron in the 

 form of a hollow cylinder, is capable of receiving more magnetism 

 than that of a solid cylinder of less diameter, but it is evident from 

 Exp. 21, that a solid bar of the same diameter as the gun barrel, and 



