The Magnetic Dial





Procure a circle of wood or ivory, about 5 or 6 inches diameter, which

must turn quite free on a stand with a circular border; on the ivory

or wood circle fix a pasteboard, on which you place, in proper

divisions, the hours, as on a dial. There must be a small groove in

the circular frame, to receive the pasteboard circle; and observe,

that the dial must be made to turn so free, that it may go round

without moving the circular border in which it is placed.



Between the pasteboard circle and the bottom of the frame, place a

small artificial magnet, that has a hole in its middle. On the outside

of the frame, place a small pin, which serves to show when the

magnetic needle is to stop. This needle must turn quite free on its

pivot, and its two sides should be in exact equilibrium.



Then provide a small bag, with five or six divisions, like a lady's

work-bag, but smaller. In one of these divisions put small square

pieces of pasteboard, on which are written the numbers from 1 to 12.

In each of the other divisions put twelve or more similar pieces,

observing that all the pieces in each division must be marked with the

same number. The needle being placed upon its pivot, and turned

quickly about, it will necessarily stop at that point where the north

end of the magnetic bar is placed, and which you previously know, by

the situation of the small pin in the circular border.



You then present to any person that division of the bag which contains

the several pieces on which is written the number opposite to the

north end of the bar, and tell him to draw any one he pleases. Then

placing the needle on the pivot, you turn it quickly about, and it

must necessarily stop at that particular number.





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