104 
ME. H. WILDE’S EXPERIMENTAL EESEAECHES 
electro-magnet (63) was considerably increased, yet this increase was only accompanied 
by a very small additional quantity of electricity from the armature ; thus showing that 
the full power of the 5-inch machine had been very nearly attained, when its electro- 
magnet was excited by the 2^-inch magneto-electric machine alone. 
'66. Having found that an increase in the dimensions of the electro-magnetic machine 
was accompanied by a proportionate and satisfactory increase of the magnetic and elec- 
tric forces, a 10-inch electro-magnetic machine was constructed ; and as its calorific and 
illuminating powers are very remarkable, some particulars respecting the machine, 
together with a few experiments made with it, may perhaps be found to possess some 
interest, especially for those physicists who are engaged in determining the quantitative $ 
relations existing between the various forces as manifested to the senses. 
67. In describing the different parts of the machine, reference will still be made to 
figures 1-9, which have been drawn to a proportionate scale. A perspective view of 
the machine complete is shown in fig. 10. Each side of the electro-magnet O, O, 
fig. 9, is made of a plate of rolled iron 48 inches in length, 39 inches wide, andl^- inch 
in thickness. The wrought-iron bars P, P, P', P', bolted to the upper and lower, 
extremities of the plates, are 6 inches wide and 2 inches thick. These bars are some- 
what longer than the width of the plates, and are secured to the sides of the magnet- 
cylinder, with the plates between them, by means of iron bolts 1 inch in diameter. The 
bridge Q extends the whole length of the bars P', P', and is made of two plates of rolled 
iron 43 inches long, 16 inches wide, and 1 J inch thick, separated from each other by an 
iron packing 3 inches in thickness, which makes the entire depth of the bridge equal 
to the width of the bars P', P'. The bridge is fixed between the side plates by means 
of long iron bolts 1 inch in diameter, extending from one side of the magnet to the other, 
as shown in the figure. All the component parts of the electro-magnet which required 
to be fitted together were planed to a true surface, for the purpose of ensuring intimate 
ferruginous contact throughout the entire mass. The total weight of the iron of the 
electro-magnet, exclusive of the magnet-cylinder, is a little more than T5 ton. 
68. Each side of the electro-magnet was coiled with an insulated conductor, consisting 
of a bundle of thirteen No. 11 copper wires, each 0T25 of an inch in diameter, laid 
parallel with each other, and bound together with a double covering of linen tape, after 
the manner adopted by Joule in the construction of his electro-magnets*. The length 
of conductor coiled round each side of the electro-magnet is 2400 feet, and the outer 
extremities of the coils are coupled up so as to form a continuous circuit 4800 feet in 
length. The inner extremities of the coils terminate in two insulated metal studs fixed 
upon the wooden top of the machine (fig. 10). The total weight of the two. coils 
is T3 ton. 
69. The magnet-cylinder consists of two masses of cast iron 50 inches in length, sepa- 
rated from each other by an interval of 5 inches, by means of blocks of brass placed at 
intervals along the top and bottom of the cylinder. All the flat surfaces of the latter, 
* Annals of Electricity, vol. v. p. 472. 
