348 ELECTRICITY, 



conductor, and forces its way, destroying whatever 

 resistance it may meet with. 



The effects of the electric matter, when it strikes 

 a building, and the method of preventing it, are 

 exemplified by an instrument called the thunder- 

 house, representing the side of a house, either 

 furnished with a metallic conductor, or not. A, 

 (Plate 20. fig. 2.) is a board about three quarters 

 of an inch thick, and shaped like the gable-end of 

 a house. This board is fixed perpendicularly upon 

 the bottom board B, upon which the perpendicular 

 glass pillar C is also fixed, in a hole about eight 

 inches distant from the basis of A. A small hole 

 I L M K, about a quarter of an inch deep, and 

 nearly one inch wide, is made in the board A, and 

 is filled with a square piece of wood nearly of the 

 same dimensions. It should be of rather smaller 

 dimensions, because it must go so easily into the 

 hole, that it may drop off by the least shaking of 

 the instrument. A wire, I K, is fastened diagonally 

 to this square piece of wood. Another wire, L H, 

 of the same thickness, having a brass ball H, 

 screwed on its pointed extremity, is fastened on 

 the board A; so also the wire M N, which is 

 shaped in a ring at N. From the upper extremity 

 of the glass pillar C, a crooked wire proceeds, 

 having a spring socket, F, through which a double- 

 knobbed wire slips perpendicularly, the lower knob 

 G of which falls just above the knob H. The 

 glass pillar C must not be made very fast into the 

 bottom board ; but it must be fixed so that it may 

 be easily moved round its own axis, by which 

 means the brass ball G may be brought either 

 nearer or farther from the ball H, without touching 

 the part E F G. Now, when the square piece of 

 wood L M 1 K (which may represent the shutter 



