Beaver Press | 1909-05-28 | Page 3 | Makes a Floating Compass

MAKES A FLO FLOATING TING COMPASS peculiarity of magnetized needle when placed in water if a thoroughly dry and clean sewing needle is very carefully laid on the surface of the water in it a basin the needle will float in spite of t the he high density of steel seven or eight times that of water on close inspection it Is found that tha t the surface of tho the water Is depressed under the needle very much as it if there were a thin film stretched over the water and lightly indented by the weight of the needle this property of liquids of offering a certain assistance to a force exerted upon their surface Is termed surface extension the magnitude of the force of surface tension varies from one liquid to another it Is greatest in the case of mercury tho the cause of the phenomenon must probably be looked for in the attraction of the liquid molecules to one another A sewing needle thus floating upon water may be used as a compass if it has previously been magnetized it will then point north and south and will maintain this position if the containing vessel Is moved about it if the needle Is 19 displaced by force it will return to its position along the mag magnetic meridian as soon as the restraint Is removed