Q. 



44 THE CANADIAN NATURALIST. [Vol. I. 



only omitted by the Congress in order to avoid the risk of con- 

 fusion ill the magnitude of the unit current with which his 

 name had been formerly associated. 



The other unit I should suggest adding to the list is that of 

 power. The power conveyed by an Ampere through the differ- 

 ence of potential of a Volt is the unit consistent with the prac 

 tical system. It might be appropriately called a Watt, in honor 

 of that master mind in mechanical science, James Watt. He it 

 was who first had a clear physical conception of power, and gave 

 a rational method of measuring it. A W^att, then, expresses the 

 rate of an Ampere multiplied by a Volt, whilst a horse-power is 

 746 Watts, and a Cheval de Vapeur 735. 



The system of electro-magnetic units would then be : — 



(1) Weber, the unit of magnetic quantity =10* 



(2) Ohm, " " resistance =10» 



(3) Volt. " " electro-motive force =10* 



(4) Ampere, " '' current =10-1 



(5) Coulomb, " '' quantity = 10-1 



(6) Watt - '• power =10^ 



(7) Farad " " capacity =10-9 

 Electricity is the form of energy best suited for transmitting 



an effect from on: place to another : the electric current passes 

 through certain substances — the metals — with a velocity limited 

 only by the retarding influence caused by electric charge of the 

 surrounding dielectric, but approaching probably under favor- 

 able conditions that of radiant heat and light, or 300,000 kilo- 

 metres per second ; it refuses, however, to pass through oxidised 

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

 rarified 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 m. m. in diameter, by nearly 5000 kilometres 

 in length, confined electrically by a coating of guttapercha about 

 4 m. m. in thickness. The electricity from a small galvanic bat- 

 tery 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 m. m. in thickness of insulating 

 material. By an improved arrangement the alternating currents 

 employed to work long submarine cables do not actually com- 

 plete the circuit, but are merged in a condenser at the receiving 



