310 BENJ. PIKE'S, JR., DESCRIPTIVE CATALOGUE. 



square piece of wood, and another of the same dimensions, 

 terminated by a brass ball, is fastened on the gable-shaped 

 board, both above and below the hole. From the upper 

 extremity of the glass pillar a crooked wire proceeds, termi- 

 nated also by a brass ball, and sufficiently long to reach 

 immediately over the ball or the wire of the board. The 

 glass pillar is loosely fixed in the bottom board, so that it 

 may move easily round the axis. It is evident that, with 

 this arrangement, a shock from a Leyden jar may easily be 

 sent over the square hole by connecting the exterior coating 

 with the wire in the gable-shaped board below it, and the 

 interior with the wire on the glass pillar which comes within 

 the striking distance of the wire in the gable-shaped board 

 below it. 



Suppose now the square piece of wood to be placed in the 

 hole in such a manner that the wire attached to it diagonally 

 shall be in contact with the wires above and below it, a shock 

 may evidently be transmitted without any disturbance taking 

 place ; but if it be put into the hole in an opposite direction, 

 so that the shock from the jar shall be obliged to pass over 

 it altogether in the form of a spark in its passage from wire 

 to wire, the concussion it will occasion will throw the square 

 piece of wood to a considerable distance from the apparatus. 

 The square piece of wood may here be supposed to repre- 

 sent a window, and the wire a continuous or broken con- 

 ductor passing by the side of it, and the violent effects pro- 

 duced by the minute quantity of electricity accumulated in 

 a Leyden jar may be considered as an humble imitation of the 

 effects of a stroke of lightning. When the passage is unin- 

 terrupted, the electricity passes quietly down, but when im- 

 peded it produces the most violent effects. 



Price, $4.00. 



Platina Point for a Lightning Conductor. The light- 

 ning conductor is an apparatus to preserve ships and build- 

 ings from the effects of lightning. It consists of a pointed 

 rod of iron or copper, half or three-quarters of an inch in 

 diameter, pointed at top, and projecting two, three, or more 

 feet above the chimney, or other highest part of the build- 

 ing, the lower end being inserted four or five feet in the 

 ground. Its action is as follows: Should lightning ap- 

 proach the building, it would most likely be drawn away 

 silently by the pointed wire ; or, if it should strike the 



