™^™ 



98 Mr. H. Wilde's Experimental Researches 



magneto-electric machine which is placed on the top of it. The 

 2|-inch magneto-electric and electromagnetic machines were 

 placed side by side upon a strong wooden base, and their arma- 

 tures were driven simultaneously from the same driving-shaft, 

 at an equal velocity of about 2500 revolutions per minute. 



60. Experiments were then made for the purpose of compa- 

 ring the quantities of electricity evolved from the magneto-elec- 

 tric and electromagnetic machines as measured approximately 

 by their heating-effects. When the alternating waves from the 

 magneto-electric machine were transmitted through a piece of 

 No. 20 iron wire, 0*04 of an inch in diameter, a length of 3 

 inches of this wire was raised to a red heat. 



61. The direct current (15) from the magneto-electric machine 

 was then transmitted through the coils surrounding the iron 

 plates 0, 0, which being united by the bridge Q, formed a 

 powerful electromagnet similar in construction to that invented 

 by Joule*, and having for its poles the two sides of the magnet- 

 cylinder. When the alternating waves from this electromagnetic 

 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 experiments, 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 3J pounds, the heating-effects of the electro- 

 magnetic machine are very remarkable. One of the most ener- 

 getic generators of dynamic electricity is that invented by Grove ; 

 and it was found from experiments made with four new cells of 

 this battery, the platinum plates of which were 6 x 3^ inches, with 

 double zinc plates well amalgamated, and charged with concen- 

 trated 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 

 electromagnetic machine. 



63. For the purpose of ascertaining in what ratio the power 

 of the electromagnetic machine would be increased by an en^ 

 largement of its dimensions, a machine was constructed double 

 the size of the one described (59), but of precisely the same pro- 

 portions. The bore of the cylinder was 5 inches in diameter, 

 and its length 25 inches. The copper wire strand surrounding 

 the electromagnet was 1170 feet in length, and weighed about 



* Phil. Mag. S. 4. vol. iii. p. 32. 



