Dodge, Mary Mapes, 1830-1905 · [New York : Scribner & Co.] · leaf 452
of thecircle will be at the needle that supports the cork.This may be easily done by removing the needle,putting the cards in place, and drawing the arcwith one leg of the compass in the hole throughwhich the needle passes. The arc is best divided by experiment. Oneway is to leave the instrument in… … A HOME-MADE HAIR HYGROSCOPE. instrument should then be put in the driest placeavailable. The thread will contract as it dries,and make the cork rotate, which in turn willmake the hand move. These two points will de-note the extremes of humidity. You may thendivide the arc according to your fancy.…
Children's literature
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