326 THE ADDRESSES, LECTURES, ETC., OF 



heat energy at certain points of the circuit when the heat rays 

 become visible, and we have the incandescence electric light. In 

 effecting a complete severance of the conductor for a short dis- 

 tance, after the current has been established, a very great local 

 resistance is occasioned, giving rise to the electric arc, the highest 

 development of heat ever attained. Vibration is another form of 

 lost energy in mechanism, but who would call it a loss if it pro- 

 ceeded from the violin of a Joachim or a Norman-Neruda ? 



Electricity is the form of energy best suited for transmitting an 

 effect from one place to another ; the electric current passes 

 through certain substances the metals with a velocity limited 

 only byithe retarding influence caused by electric charge of the sur- 

 rounding dielectric, but approaching probably under favourable 

 conditions that of radiant heat and light, or 300,000 kilometres 

 per second ; it refuses, however, to pass through oxidised sub- 

 stances, glass, gums, or through gases except when in a highly 

 rarefied condition. It is easy therefore to confine the electric 

 current within bounds, and to direct it through narrow channels 

 of extraordinary length. The conducting wire of an Atlantic 

 cable is such a narrow channel ; it consists of a copper wire, or 

 strand of wires, 5 mm. in diameter, by nearly 5,000 kilometres in 

 length, confined electrically by a coating of gutta-percha about 

 4 mm. in thickness. The electricity from a small galvanic battery 

 passing into this channel prefers the long journey to America in 

 the good conductor, and back through the earth, to the shorter 

 journey across the 4 mm. in thickness of insulating material. By 

 an improved arrangement the alternating currents employed to 

 work long submarine cables do not actually complete the circuit, 

 but are merged in a condenser at the receiving station after having 

 produced their extremely slight but certain effect upon the receiv- 

 ing instrument, the beautiful syphon recorder of Sir William 

 Thomson. So perfect is the channel and so precise the action of 

 both the transmitting and receiving instruments employed, that 

 two systems of electric signals may be passed simultaneously 

 through the same cable in opposite directions, producing inde- 

 pendent records at either end. By the application of this duplex 

 mode of working to the Direct United States cable under the 

 superintendence of Dr. Muirhead, its transmitting power was 

 increased from twenty-five to sixty words a minute, being equiva- 



