IGNIS-FATITUS. 35 



any mischief they do. Thunder-storms cool the 

 atmosphere and purify it from noxious vapours. 

 The rain which usually accompanies thunder and 

 lightning promotes the fertility of the soil and 

 the growth of plants. 



Men have a contrivance for securing build- 

 ings from the effects of lightning. A long iron 

 rod, called a lightning-conductor, is erected close 

 to the house, in such a manner that the lower 

 end reaches into moist earth, and the upper rises 

 above the ridge of the roof. A rod of this kind 

 attracts the electric matter, and conducts it down 

 to the earth without injury to the building. A 

 house surrounded by tall trees is rarely struck by 

 lightning, because the lightning is attracted by the 

 trees. Remember not to take shelter under trees 

 during a thunder-storm. 



O Sound is transmitted at the rate of 1142 feet, 

 or 380 yards, in a second ; the distance of light- 

 ning may therefore be calculated,' by accurately 

 observing the time which intervenes between 

 the flash, and the thunder which follows it. 



IGNIS-FATUUS FALLING STARS AURORA 



BOREALIS. 



We have all heard of lights, commonly called 

 Will-with-a-wisp, or Jack-with-a-lantern, but 

 known to scientific men by the name of ignis^ 

 fatuus. These lights are seen most frequently 



