The outlines of physics: an elementary text-book . e shape of whichvaries with the experiment to be performed. 255. Experiment 78. — Testing Bodies of Low Permeability. Apparatus : (1) An electromagnet. This may be of small size, like that shown in Fig. 254, the coils of which are only 5 cm. long. (2) The bichromate battery. (3) Some minute bars of bismuth, tellu-rium, zinc, lead, glass, etc., not more than 1cm. long, and •! or -2 cm. in diameter. Themetals may be made into such bars by meltingin a crucible, and sucking them up into thebore of glass tubes. The glass, when cold,may be broken aw
The outlines of physics: an elementary text-book . e shape of whichvaries with the experiment to be performed. 255. Experiment 78. — Testing Bodies of Low Permeability. Apparatus : (1) An electromagnet. This may be of small size, like that shown in Fig. 254, the coils of which are only 5 cm. long. (2) The bichromate battery. (3) Some minute bars of bismuth, tellu-rium, zinc, lead, glass, etc., not more than 1cm. long, and •! or -2 cm. in diameter. Themetals may be made into such bars by meltingin a crucible, and sucking them up into thebore of glass tubes. The glass, when cold,may be broken away. Procedure : Hang the bars in succession between the poles of the electromagnet,using as a suspension as fine a fiber of cocoon silk as you can in each case whether the ^bar tends to set itself along the linesof force or perpendicular to them. Bismuth and tellurium should show marked diamagnetic others, although classed as diamagnetic, more frequently areslightly magnetic from the presence of iron as an Fig. 254. MEASUREMENT OF CURRENT 291 CHAPTER XXIX THE MEASUREMENT OF CURRENT, ELECTROMOTIVE FORCEAND RESISTANCE 256. The Galvanometer. — The arrangement described inChapter XXVII, where the coil of wire surrounds a floatingneedle, contains all the essential features of the instrument known as the galvanometer. This ins]trument, which we havealready used in certain experi-ments in Heat, and the construc-tion of which is described insome detail in Appendix VI,consists of a suspended magnetwhich is placed in the axis of acoil of wire, and is therefore de-flected from its north and soilthposition whenever a currentflows through the coil. Thecoil of wire may consist of oneor many turns, according to thestrength of the current to bemeasured. For the measure-ment of large currents, thegalvanometer is frequently giventhe form shown in Fig. this instrument, which iscalled the tangent galvanometer, because the tangent of theangle throu
Size: 1437px × 1738px
Photo credit: © The Reading Room / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1800, bookdecade1890, bookpublishe, booksubjectphysics
