144 THE EEASON WHY. 



' The voice of thy thunder was in the heaven i the lightnings lightened th 

 world, the earth trembled and shook." PSALM LXVII. 



633. What is magnetism ? 



Magnetism is the electricity of the earth, and is characterised 

 by the circulation of currents of electricity passing through tha 

 earth's surface. 



634. Wliat are magnetic lodics ? 



Magnetic bodies are those that exhibit phenomena which show 

 that they are under the influence of terrestrial electricity, and 

 which indicate the direction of the poles, or extreme points, of 

 magnetic force. 



635. What is Galvanism ? 



Galvanism is the action of electricity upon animal bodies, and i? 

 BO called from the name of its first discoverer, Galvani. 



636. Wliat it Voltaic electricity ? 



Voltaic electricity is the electricity that is developed during 

 chemical changes, and is so called after Volta, who enlarged upon 

 the theory of Galvani. 



637. What are the differences between mechanical, or 

 fractional electricity, Voltaic electricity, Galvanism, and 

 magnetism ? 



Frictional electricity is electricity suddenly liberated under the 

 effects of the motion, or the mechanical disturbance of bodies. 



Voltaic electricity is a steady flow of an electric current, arising 

 from the gradual changes of chemical phenomena. 



Galvanism and Voltaism are almost identical, since the latter is 

 founded upon, and is a development of, the former. But the 

 term Galvanism is frequently used when speaking of the develop- 

 ment of electricity in animal bodies. 



Magnetism is the electricity of the earth, and is understood tc 

 imply the fixed electricity ofterrestial bodies. 



Man knows not what electricity is ; yet, by an attentive observance of its 

 effects, he avails himself of the power existing in an unknown source, and 

 produces marvellous results. When the Grecian philosopher, Thalcs, sat 

 rubbing a piece of amber, and watching the attraction of small particles of 

 matter to its surface, ho little knew of the mighty power that was then 

 whispering lo him its offer to serve mankind. And when Franklin, with the 



