ELECTRIC EFFECTS. 225 



able thermal effects may be obtained. Houses are some- 

 times set on fire by lightning. 



366. Luminous Effects. The luminous effects of 

 electricity are due to discharges through bad conductors. 

 The electric spark is the most familiar example. The 

 glow seen when electricity escapes from a pointed con- 

 ductor in the dark, and the various forms of lightning, 

 render familiar the luminous effects of electricity. ( 371, 

 [24H31]). 



367. Magnetic Effects. A common needle may 

 be magnetized by winding about it a covered copper wire 

 and discharging a Leyden jar through the wire. The 

 magnetic effects of electricity are better and more com- 

 monly shown with Voltaic electricity. ( 392.) 



368. Chemical Effects. The electric spark may 

 be made to produce chemical combination or chemical 

 decomposition. Ammonia gas (NH 3 ), or carbonic acid 

 gas (C0 2 ), may be decomposed by passing a series of sparks 

 through it. A mixture of oxygen and hydrogen may be 

 caused to enter into chemical union by the electric spark, 

 the product of the union being water (H 2 0). ( 371 [35].) 



369. Mechanical Effects. The piercing of the 

 glass walls of an overcharged Leyden jar affords a good, 

 though expensive, illustration of the mechanical effects of 

 electricity. Trees and telegraph poles shattered by light- 

 ning are not unfamiliar. ( 371 [32]-[34].) 



(a.) Charge a Leyden jar. In discharging it, hold a stiff card 

 between the knob of the jar and the knob of the discharger. A 

 hole will be pierced through the card. By the side of this hole in 

 the card make another with a pin. Any one can tell by examina- 

 tion of the pin hole from which side of the card it was pierced ; it 

 is burred on only one side. Not so with the perforation made by 



