RECENT WONDERS OF ELECTRICITY. 789 



an Apps's induction coil, to which can be joined up vacuum tubes of 

 various kinds, and through which the currents produced by the hand 

 dynamo-machine will be passed. [A beautiful collection of vacuum 

 tubes, fitted with various rarefied gases, was then shown, while the 

 lights were turned down.] In those effects we have the result of elec- 

 tricity passing through air, and gases of extreme tenuity, and also an 

 indication of the way in which electricity produces heat and, there- 

 fore, light in gaseous matter. All instances of artificial lighting or 

 heating are simply due to the fact that we are able to produce heat, 

 and heat of a very high temperature. It is a curious fact that all 

 matter, whether metal or porcelain, carbon or lime, begins to emit 

 light at precisely the same temperature, which closely approaches 

 1,000 Fahr., or, to be accurate, I believe it is 980 Fahr., so that, 

 whenever it is possible by any means to raise any material to that 

 temperature, light is emitted, and the intensity of light increases, 

 until, in the case of carbon, when about 4,000 Fahr. is reached, the 

 material is destroyed. In platinum, a lower figure (3,082) represents 

 the point of fusion. To obtain this very high temperature by electric 

 currents, we must utilize higher means of producing the electricity 

 than I have hitherto shown you. In the battery I have just used, the 

 electric current was produced by the combustion of zinc ; but now I 

 want to explain to you how, as I said, muscular power was converted 

 into electric energy. The reason is simply due to the fact discovered 

 by Faraday, that whenever a wire or conductor moved through the 

 sphere or field of a magnet, it became electrified. I take up the brass 

 rod before me and move it rapidly, and by doing so have, to a certain 

 extent, electrified it by causing it to pass through the magnetic field 

 of the earth. The earth is an enormous magnet a fact which we 

 know, because our compasses guide the mariners across the deep. The 

 air in this room is under the influence of the earth's magnetism ; and 

 if I move a wire or rod within that influence, at right angles to the 

 lines of magnetic force, I cause it to be electrified, but only to an ex- 

 cessively small extent. The strength of the current produced depends 

 upon the strength of the magnetic field, and upon the velocity with 

 which the conductor moves across the field. Instead of having only 

 one rod, or one wire, we have in this hand-machine an arrangement of 

 a thousand turns of wire ; instead of having the weak magnetism of 

 the earth, we have the powerful field of permanent magnet ; and, in- 

 stead of causing it to move through the air by the velocity of my arm, 

 we apply multiplying gear, which, as you see, imparts velocity to it of 

 great rapidity. Thus motion, through a magnetic field, produces an 

 electro-motive force. There never can be a continuous electro-motive 

 force without some source of energy. Here we have mechanical 

 energy expended, and all the conditions for the production and main- 

 tenance of a current. Energy expended in one point must be found 

 in some form in another point. If it is not utilized, it is wasted. 



