THE HEW ELECTRO-MAGNETIC MACHINES. 
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change common dynamic or motive power into electricity. To 
this end a steam-engine of 15-horse power is employed to drive, 
by means of leather bands, the armatures of the magneto- 
electric (a) and electro-magnetic (x, d) portions. The armature 
( i g ) is the first or magneto-electric machine ( a ) ; is driven at the 
rate of 2,000 revolutions per minute ; and as both portions of the 
armature are thus presented to the poles of the magnetic battery 
during each revolution, 4,000 waves of electricity are transmitted 
per minute to the steel studs of the great electro-magnet ( x , w, u) 
exciting it to intense action and keeping it constantly highly 
charged with magnetic influence. Whilst so excited its huge 
armature revolves with the rapidity of 1,500 revolutions per 
minute, thus supplying 3,000 waves of electrical force for any 
required practical purpose, such as the maintenance of a 
powerful light, or the heating of metal bars or wire, or the ex- 
ercise of magnetic attraction, this great electro -magnet being 
capable under the last condition of sustaining a weight of 50 tons. 
The armatures used in this electro-magnetic portion measure 
52 inches in length and are of two kinds, one for intensity, used 
in the production of light, the other for quantity, used for the 
production of heat. The intensity-armature is wound round 
with 376 feet of insulated cable of 13 strands of covered wire 
the same as that wound round the electro -magnet itself ; the 
quantity-armature has an insulated conductor composed of 4 
plates of copper, each 67 feet in length, 6 inches wide, and j^th 
of an inch in thickness, superposed in metallic contact. The weight 
of the armature-intensity coils is 232 lbs. ; that of the insulated 
plates in the quantity-armature 344 lbs., and its total weight 
more than a quarter of a ton. The principle developed by Mr. 
Wilde is that by charging the large electro-magnet by means 
of the magneto-electric battery with as nearly as possible the 
quantity of magnetism it is capable of imbibing, and by means 
of this adjunct maintaining constantly this full charge, the maxi- 
mum electrical current can be drawn off by the Siemens’ arma- 
ture (s' s') from the electro-magnet* ( x , u, u ). The increase of 
power so obtained is continuously as far greater than that which 
is obtainable from revolving the same armature in an uncharged 
or partially charged magnet as the cube of the saturation is to 
the cube of the residual magnetism naturally contained in the 
iron of the magnet. 
The experiments performed with Mr. Wilde’s large machine, 
during the time it was stationed in the lower library of the 
Eoyal Society, were most interesting and marvellous, although 
necessarily they were restricted in variety by the absence of 
auxiliary philosophical apparatus of anything like sufficient size 
or capacity for receiving such an unrivalled stream of electrical 
force, and consequently the chief display of its powers consisted 
