Applied Science 797 



trical horse-power, for transmission to Leghorn, Florence, and 

 Pisa, to which points the steam itself obviously could not be piped. 



What a Current of Electricity is 



What we know to-day of the nature and inter-relationship 

 of electricity and magnetism has been explained in a previous 

 chapter. The electro-magnet, in some form or another, is the basis 

 of all machines for generating electric currents by mechanical 

 power called dynamos, of electric motors, induction coils, and 

 other appliances. The electro-magnet is at the bottom also of all 

 modern electric telegraphy and telephony. 



It was the crowning discovery of Michael Faraday that a 

 current of electricity could be induced in a closed coil or ring of 

 wire by moving it towards or away from a magnet in other 

 words, by moving it across a magnetic field. Faraday was also 

 responsible for the first dynamo. What is a magnetic field? An 

 electric current is a flow of electrons, passing from atom to atom. 

 If we put zinc and copper together we get a mild current of elec- 

 tricity; the atoms of zinc are particularly disposed to part with 

 their electrons, and these electrons pass to the atoms of copper; 

 their passage is a "current" an atom is giving up an electron to 

 its neighbouring atom. If the metals copper and zinc are im- 

 mersed in certain chemicals, which slowly dissolve the zinc, and the 

 two metals are connected by a copper wire, the current is stronger, 

 there is a brisker flow of electrons (see p. 270) . Copper, in other 

 words, is a good "conductor." Now we have also seen (p. 273) 

 that there is no movement of electrons without their creating an 

 attendant field of energy; a magnetic force due to the electric 

 current exists in circles around the wire, and results in an ether 

 disturbance, or strain. Thus the space around the path of an 

 electric current is filled with lines of magnetic force, and we have 

 what is called a "magnetic field." 



Faraday therefore found the means of creating an electric 



