. The Philosophical magazine; a journal of theoretical, experimental and applied physics. the one beingoutside the clock-case while the other is inside),and from the expense of the mercurial pendu-lum. Considering it possible to make a com-pact pendulum rod which shall not possess thedisadvantages of the others, and that such anone would still be a desideratum, I shall pro-ceed at once to the description, after havinggiven the data upon which the calculations arefounded. The average expansion of iron, as taken fromthe experimentsof Lavoisier and Laplace, Bor-da, Smeaton, Troughton, and Dulong
. The Philosophical magazine; a journal of theoretical, experimental and applied physics. the one beingoutside the clock-case while the other is inside),and from the expense of the mercurial pendu-lum. Considering it possible to make a com-pact pendulum rod which shall not possess thedisadvantages of the others, and that such anone would still be a desideratum, I shall pro-ceed at once to the description, after havinggiven the data upon which the calculations arefounded. The average expansion of iron, as taken fromthe experimentsof Lavoisier and Laplace, Bor-da, Smeaton, Troughton, and Dulong and Petitbetween the temperatures of 32° and 212° F.,for every 1-000000000 is -00124869, or for 1°Fahr. is -000006937. The expansion of steelspring for 1° Fahr. is -00000761 according toMuschenbroek ; and that of hammered zinc for1° Fahr. is -00001672 according to Smeaton. If the pendulum be constructed as usual ofthree inches of watch spring, and the remain- ider of iron wire, the expansion for 1° of Fahrwill be 3 inches steel -000022830 36-139290 iron -000250600 -000273130 Prof. Olmsted oti the Gold Mines of North Carolina. 375 which would be counteracted by 16*35 inches of zinc. But asthis cannot be applied without adding more iron, the zincmust be increasecl by so much as will also counteract that ad-dition : and yet the zinc must not be greater or less in lengththan the iron added. The exact quantity I make to be 2792inches. The expansion of pendulum rod will then be for 1° in. steel -00002283036-139290 iron -00025060027-92 iron -000193542 67-059290 in. -000466972 of 27-92 inches zinc will be •000466822. Having determined the length of zinc necessary, I apply itthus :—The pendulum rod is made as usual in common clocks,with three inches of steel spring attached to an iron wire,having a foot firmly fastened to it;—a tube of zinc 27-92inches long, is slid over this rod and fastened to the foot: aniron tube is now put over this zinc tube, and at the to
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