134 THE EEASON WHY. 



" Yea, he sent out his arrows, and scattered them ; and he shot out lightnings 

 and discomfited them." PSALM xvin. 



particles of matter which were drawn towards their substances. If 

 a bar of iron were excited, instead of a stick of wax, electricity 

 would be equally developed ; but the iron, being a good conductor, 

 would pass the electricity to the hand of the operator as fast as it 

 accumulated, and the equilibrium would be undisturbed. 



577. What is the effect when electricity, in considerable 

 force, seeks its equilibrium, but meets with insulating bodies ? 



The result is a violent action in which, intense heat and light 

 are developed, and in the evolution of which the electric force 

 becomes expended. 



578. What is the cause of electric sparks ? 



The electric force, passing through a conducting body to find its 

 equilibrium, is checked in its course by an insulator, and emits a 

 spark. 



579. What produces the electric light? 



Currents of electricity pass towards each other along wires at the 

 ends of which two charcoal points are placed. As long as the char- 

 coal points remain in contact, the electric communication is complete, 

 and no light is emitted, but, when they are drawn apart, intense 

 heat and light are evolved. 



FigS. 17 & 18.-SHOWISG THE EFFECT OF THE UNIOX AND THE SEPARATION 

 OF THE CHARCOAL POINTS. 



580. What is the cause of lightning ? 



Lightning is the result of electrical discharges from the clouds. 



581. What developes electricity in the clouds ? 

 Evaporations from the surface of the earth; changes of 



temperature in the atmospheric vapour ; chemical action upon the 

 earth's surface; and the friction of volumes of air of different 

 densities against each other. 



