Allen, Charles Ricketson, 1862- [from old catalog] · New York, H. Holt and company · leaf 245
g ; and the needle itself a piece of magnetizedknitting-needle short enough to swing freely in the frame. Apiece of writing-paper is cut in the form shown, and the needlestuck through the lower part. A second needle, for a pointer, isstuck through the upper part. The two needles should be about 232… … needle, which is then suspended by a hair, or a thread ofuntwisted silk, so that it swings freely within the coil. Ifdesired, a scale may be marked on a circular piece of card-board,and laid on the coil, but it is not necessary. In the diagram thecard shown above the indicator swings with it and…
Physics
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