320 
THE STORAGE OF ELECTRICITY. 
By J. MUNRO, C.E. 
T HE last five years have been marked by an extraordinary 
development of electrical invention. They have given 
ns the speaking telephone and the microphone, which may now 
be found working conjointly in transmitting all varieties of 
human speech by wire in every clime, from London to Hono- 
lulu, and from Stockholm to Melbourne. They have given us 
the duplex and quadruplex modes of sending an ordinary tele- 
gram, so that two, and even four messages of entirely different 
import may he passed through a single overland line or sub- 
marine cable simultaneously, without either jostling or ob- 
literating one another. They have given us the electric light 
to illuminate our streets, factories, and homes with artificial 
sunshine ; and they have given us the means of conveying 
power by electricity to great distances, so that in the future we 
may drive our looms and speed our trains by the energy of 
waterfalls among the hills, and light our beacons by the fury of 
the waves which break around them. A thousand possibilities 
of electric labour open on our sight, and in a few minutes we 
can prophesy what the next fifty years will fulfil. 
The application of electricity to lighting and motive pur- 
poses which promises so largely for the future, is chiefly due to 
the recent perfection of the dynamo-electric machine, whereby 
electricity is generated in a coil of wire rapidly rotated in the mag- 
netic space between the opposed poles of two powerful electro- 
magnets. Unlike the clumsy and troublesome voltaic battery, 
it is compact and portable, and yields a steady current so long 
as the coil is rotated. This current may he conducted by wires 
to an electric lamp, and there transformed into a splendid light ; 
it may be used instead of a battery- current to transmit tele- 
grams, after the fashion of the great Western Union Telegraph 
Company of America ; or it may be sent through a second 
