jeiectric Generators. 73 



namo there is a discharge every time the elec- 

 tromagnet of the armature cuts through the 

 lines of force of the magnetic field, and in the 

 galvanic battery every time a molecule is 

 broken up and its little measure of energy is 

 set free. In the dynamo the pulsations are 

 so far apart as to make a musical tone of not 

 very high pitch, but in the galvanic battery 

 the pitch of the tone, if there is one, would re- 

 quire a special ear to hear it one tuned, it 

 may be, up near the rate of light vibration. 



There are two types of dynamo, one generat- 

 ing a direct and the other an alternating cur- 

 rent. (By alternating we mean first a positive 

 and then a negative current impulse.) We can- 

 not enter into a technical description of the 

 dynamo in a popular treatise such as this. 



The dynamo has evolved from the germ dis- 

 covered by Faraday, till to-day it is a machine, 

 the construction of which requires the high- 

 est .-lass of engineering skill. When in action 

 it seems like a great living presence, scatter- 

 ing its energy in every direction in a way 

 that is at once a marvel and a blessing to man- 

 kind. But we must not give all the credit 

 t<> the dynamo. As the moon shines with a 

 reflected light, so the dynamo gives ofT energy 

 t)J a power delegated to it hy tin- steam-engine 

 that rotates it. and the steam-engine owes its 

 life to the burning coal, and the burning coal 

 \B only giving up an energy that was 



