IN MAGNETISM AND ELECTRICITY. 
103 
nating waves from this electro-magnetic machine were transmitted through the same- 
sized iron wire as was used in the preceding experiment, 8 inches of it were melted, and 
a length of 24 inches was raised to a red heat. 
62. A comparison of the heating effects of the two machines, as found by these expe- 
riments, brings out the important fact, that a much greater amount of electricity is 
evolved from the electro-magnetic machine than is evolved simultaneously from the 
magneto-electric machine. Moreover, considering the smallness of the quantity of iron 
of which the armature was made (only five pounds), and of the copper wire surrounding 
it, the weight of which was only 3^- pounds, the heating effects of the electro-magnetic 
machine are very remarkable. One of the most energetic generators of dynamic elec- 
tricity is that invented by Grove, and it was found from experiments made with four 
new cells of this battery, the platina plates of which were 6 x 3-| inches, with double 
zinc plates well amalgamated, and charged with concentrated nitric acid and a strong 
solution of sulphuric acid, that ten cells of this powerful arrangement would be required 
in order to produce the same heating effects as those produced by the electro-magnetic 
machine. 
63. For the purpose of ascertaining in what ratio the power of the electro-magnetic 
machine would be increased by an enlargement of its dimensions, a machine was con- 
structed double the size of the one described (59), but of precisely the same proportions. 
The bore of the cylinder was 5 inches in diameter, and its length 25 inches. The 
copper wire strand surrounding the electro-magnet was 1170 feet in length, and weighed 
about 390 lbs. The armature of this machine was coiled with an insulated copper 
strand 84 feet in length, the weight of which was about 28 lbs. 
64. When the electro-magnet of the 5-inch machine was excited by the 24-inch mag- 
neto-electric machine, the armature of the 5-inch machine being. driven at about 2000 
revolutions per minute, the electricity from it melted 15 inches of No. 15 iron wire 
0-075 of an inch in diameter. Now it was found that a piece of No. 15 iron wire 
15 inches in length, was about seven times the weight of 8 inches of the wire melted by 
the 2^-inch electro-magnetic machine (61) ; and as the 5-inch machine was about eight 
times the weight of the 24-inch electro-magnetic machine, the increase of power of the 
5-inch machine, as measured by its heating effects, appears to me to be nearly in direct 
proportion to the increase of its cubical dimensions, after allowance has been made for 
the diminished speed at which the armature was driven, together with the small increase 
of power which might have been obtained had the electro-magnet been excited by a more 
powerful magneto-electric machine. 
65. For the purpose of learning to what extent the power of the electro-magnetic ma- 
chine might be increased by an exaltation of the magnetism of the electro-magnet, with- 
out changing the speed at which the armature was driven, the electro-magnet of the 
5-inch machine was excited by the direct current from the 2^-inch electro-magnetic ma- 
chine (59), the latter being in its turn excited by the 2^-inch magneto-electric machine 
(58). On making the experiment, it was found that although the magnetism of the 
