ELECTRICAL APPARATUS. 



311 



building, the conductor would convey it to the earth Fi s- 37 - 

 without its doing- any injury. 



The most usual way that lightning rods terminate 

 is by merely pointing the rods, sometimes gilding 

 them ; the action of the weather on these in a short 

 time destroys the point, and the utility of the rod is 

 in part, or wholly destroyed. To remedy this defect, 

 a copper cone about six inches long, terminated in a 

 platina point (Fig. 370), about one inch in length, is 

 fastened to the top of the rod ; this metal will undergo 

 no change by the action of air and water, and will not 

 even tarnish, however long exposed to the action of 

 the weather, and is always used where rods are put 

 up in the best manner. 



Price, each, $4.00 ; small, $3.00. 



Powder House. An 

 electrical apparatus, to 

 show, in an amusing man- 

 ner, the firing of gunpow- 

 der by electricity, and 

 thereby proving the effect 

 of lightning upon buildings 

 in setting them on fire. 



Fig. 371 represents a 

 perspective view, the side 

 next the eye being omitted 

 that the inside may be 

 more conveniently seen. 



The front is fitted up like the thunder house and used in 

 the same manner. The house itself is made of seven pieces 

 of mahogany, joined together by hinges, so as to be capable 

 of falling flat on the table ; a small projecting ridge along 

 the top of the roof holding it up until the powder is fired. 

 A is a ball of brass with wire reaching partly down the 

 house, and across it, inside to the brass top of the table c. 

 This has the gunpowder placed upon it. Immediately 

 above the powder is a second ball, which leads by a wire to 

 the outside of the house at the opposite end, passing 

 through the wood at the end of the house. Then follows 

 the wetted thread, E, and afterwards the chain, B. Passing 

 an electrical shock from A to B, the powder will be fired 

 and the house thrown down. 



