518 



ness, be laid flat upon a table, and pressed down by a 

 weight, and the points of the wires be set opposite to each 

 other and against the under edge of the glass, so that the 

 electricity may pass beneath it, the charge of a large jar 

 transmitted in this way will break the glass into innu- 

 merable fragments, and even reduce a portion into an 

 impalpable powder. If the mouth of a small mortar 

 made of ivory, with a cavity of half an inch diameter, 

 and an inch deep, stopped by a cork, fitted so as to close 

 the aperture accurately, yet without much friction, and 

 if two wires be inserted through the sides of the mortar 

 so that their points within the cavity, be separated by an 

 interval of about a quarter of an inch, a strong charge 

 being sent through the wires will expand the air within 

 the cavity so suddenly as to project the cork to some dis- 

 tance. 



' Solid bodies of a porous texture, such as wood, are 

 easily torn asunder by an electric charge. If two holes 

 be drilled in the opposite ends of a piece of wood, about 

 half an inch long, and a quarter of an inch thick, and 

 the ends of two wires inserted in the holes, so that their 

 points may heat the distance of a quarter of an inch, on 

 passing a strong charge the wood will be split in 

 pieces. Stones, loaf-sugar, and other brittle and imper- 

 fectly conducting substances, may be broken in a simi- 

 lar way. 



'Place a piece of dry writing paper upon the table of 

 the universal discharger, and having removed the balls 

 from the ends of the sliding wire?, press the points of the 

 wires against the paper at the distance of two inches from 

 each other, if a powerful shock be now sent through the 

 wires, the paper will be torn in pieces. If a number of 

 wafers be placed on the table instead of paper they will 

 be dispersed in a curious manner, and many of them 

 broken into small fragments. 



The thunder house. This is an apparatus designed to 

 show the efficacy of a lightning rod in preventing the 

 violent effects of lightning. It contains in the side of a 

 little wooden house, a square piece of wood, which when 

 the little lightning rod is interrupted in its course, is 

 thrown out with violence. 



