ELECTRICAL APPARATUS. 



307 



sized pieces of thin tin-foil, so arranged 

 that the order of succession shall be 

 preserved throughout, viz. zinc, silver, 

 paper, zinc, silver, paper, etc. ; about 

 one thousand pairs of such discs, in- 

 closed in perfectly dry glass tubes, ter- 

 minated at each end with brass caps 

 and screws, to press the plates tight 

 together, will produce an active arrange- 

 ment ; the positive end of one column is 

 placed lowest, and the negative end of 

 the other, their upper extremities being 

 connected by a wire, that they may be 

 considered as one column. A small bell 

 is situated between each extremity of 

 the column and its insulating support ; a brass ball is sus- 

 pended by a thin thread of raw silk, so as to hang midway 

 between the bells, and at a very small distance from each 

 of them. For this purpose the bells are connected, during 

 the adjustment of the pendulum, by a wire, that their at- 

 traction may not interfere with it ; and when this wire is 

 removed, the motion of the pendulum commences. The 

 whole apparatus is placed upon a circular mahogany base, 

 in which a groove is turned to receive the lower edge of a 

 glass shade, with which the whole is covered. 



Price, $20.00. 



Thunder House. (Fig. 367.) This in- 

 genious article is made of an upright piece 

 of baked mahogany, formed like the gable 

 of a house, as B B, and placed upon a 

 wooden stand. A wire marked c, runs 

 downwards throughout its whole length. 

 It is terminated above by a ball, A, which 

 being unscrewed shows a point beneath it. 

 In one or two parts of the gable are square 

 pieces of wood cut out. These are a quar- 

 ter of an inch thick, and one inch square 

 on the side. They are shown at D and F ; 

 are made so as to fit loosely into a hole 

 cut partly into the gable to receive them, and have a wire 

 running across each, so placed, that putting in the pieces in 

 one way, the wires shall with c E form a continuous and 



