90 PRACTICAL LESSONS IN SCIENCE. 



the air and lightning and thunder follow, and sometimes with- 

 ered trees, burned buildings, and loss of life is the result. 



As some protection from accidents from this cause lightning 

 rods have been devised. They consist of metal, usually of iron, 

 although copper is a better material. The lightning rod should 

 be of ample size, and attached securely and closely to the build- 

 ing and to all metallic pipes about the building. It should reach 

 downward to ground that is permanently moist, and it would 

 be better if it terminated in a broad plate of metal. It should 

 extend upward for some distance above the building and termi- 

 nate in bright, sharp points. When first invented it was thought 

 necessary to separate the lightning rod from the building, but it 

 was soon discovered that it was better to connect the whole 

 building with the rod, which discharges electricity so rapidly 

 that no accumulation occurs to cause dangerous results. The 

 effects of lightning, so well known to all, show that electricity 

 can do mechanical work, as in the tearing of trees, shattering of 

 walls, etc. 



To Doctor Franklin belongs the immortal honor of provingthe 

 identity of electricity and lightning. A kite was the simple instru- 

 ment which he employed. Having made a kite by stretching a silk 

 handkerchief over two sticks in the form of a cross, he went out 

 into a field accompanied only by his son; raised his kite; fast- 

 ened a key to the lower end of its hempen string ; insulated it by 

 fastening it to a post by means of a silk cord, and anxiously 

 awaited the approaching storm. A dense cloud, apparently 

 charged with lightning, soon passed over the spot where he 

 stood, without causing his apparatus to give any sign of elec- 

 tricity. He was about to give up in despair, when he caught 

 sight of some loose fibers of the hempen cord bristling up as if 

 repelled. He immediately presented his knuckle to the key, and 

 received an electric spark. The string of his kite soon became 

 wet with the falling rain ; it was then a better conductor, and he 

 was able to obtain an abundance of sparks from the key. By 

 this experiment he furnished a decisive proof of the identity of 

 lightning and electricity. 



