The Royal Socrety Sotree. 433 
sliding in good metallic contact with the copper plates, and 
forming the polar terminals of the entire machine. By a 
most simple contrivance, the enormous stream of electricity 
is turned on or off at will. A handle, very like that of a tap 
handle, protrudes from the top of the experimental table ; 
at the base of its shaft below, is attached a bar of copper. 
When the bar is turned across the conductors, short con- 
tact is made, and no electric current passes on to the ter- 
minals ; but when this bar is turned parallel with the con- 
ductors, it rests inert between them, and the electricity 
passes on in its longer course. The weight of the large 
electro-magnet alone, is nearly three tons, and the total 
weight of the whole machine, is four and a half tons. The 
effects produced are astounding. With the quantity-arma- 
ture running the evolution of dynamic electricity is so 
enormous, that pieces of cylindrical iron rod 15 inches in 
fength, and fully a quarter of an inch in diameter, were 
melted down in a few minutes, and copper wire of *125 inch 
diameter as quickly shared the same fate. A beautiful 
sight it was, to see the thick iron bar between the poles 
reek, glow vermilion red, become tawny, orange, yellow, 
then white, and then perfectly incandescent, and finally to 
trickle with tears of molten metal that ran along and 
dropped. In the same way long loops of stout iron wire 
such as is used for fencing, more than a couple of yards in 
length, were held by a hook, and the current of electricity 
passed through ; the whole loop soon became incandescent, 
and tears of melted white hot metal trickled fast and quickly 
and ran along its length, spattering on the iron experi- 
mental table, and sometimes falling in countless sparks 
upon the floor. With the intensity armature 21 feet of 0°65 
inch iron wire may be made red hot. When the 10-inch 
electro-magnetic machine is charged with a direct current 
from the small magneto-electric battery, the development 
of magnetic force is unprecedented, and is equal to the 
lifting of 50tons. During the evening a large bar of pla- 
tinum was laid across the poles. The glow was magnifi- 
cent ; but it suddenly disrupted under the powerful current 
into numerous fragments. Outside the building the effect 
of the light was very great; the lamps were paled almost 
into the hue of very pale-brown paper; the smallest print, 
such as that of the popular sixpenny editions of Cooper's 
novels, and even smaller, was perfectly legible at the en- 
trance gateway ; and the flame of a piece of lighted paper 
had, at that distance, its image distinctly shadowed on a 
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