3(')0 ELECTRICITY. 



experiment, care must be taken that the charge be 

 very weak, otherwise the tube will burst. 



In a common drinking-glass almost full of water 

 (Fig. 16.) immerse two knobbed wires, so bent 

 that their knobs may be within a little distance of 

 one another in the water. If one of these wires be 

 connected with the outside coating of a pretty 

 large jar, and the other wire be touched with the 

 knob of it, the explosion which must pass through 

 the water from the knob of one of the wires to that 

 of the other will disperse the water, aud break the 

 glass with a surprizing violence. This experiment 

 is dangerous, if not conducted with great caution. 



The Powder-House. 



Fig. 17. is an ingenious contrivance, and well 

 adapted to the purpose : the front is fitted up like 

 the thunder-house; it is generally made seven or 

 eight inches long, and nearly the same height to 

 the top of the roof; the side, and that half of the 

 roof next the eye, is omitted in the figure, that the 

 inside may be more conveniently seen. The sides, 

 back, and front of the house are joined to the bot- 

 tom by hinges ; the roof is divided into two parts, 

 which are also fastened by hinges to the sides; the 

 building is kept together by a ridge fixed half way 

 on one side of the roof, so that when the building 

 is put together, the other half of the ridge reaches 

 over the other half of the roof, and holds it to- 

 gether. Within the house there is a brass tube l£ 

 inch long, and five-eighths of an inch in diameter, 

 screwed on a pedestal of wood; into the side of 

 this brass tube is screwed a wire, which goes 

 through one-eighth of an inch or better; the other 

 end, by means of a chain, has a communication to 



