. Laboratory exercises in elementary physics. 18 uncovered copper wireruns up from binding-post a, and to it are attached the ends ofthe naked iron and copper wire, as indicated. The number oflengths of these depends upon the size of wires. For the slidingcontact, the end of a piece of No. 18 copper wire may be ham-mered out flat, and then bent into the form of a hook. An Eng-lish binding-post is best. Sensitive Galvanometer. (See Fig. 115.)—The frame is of woodabout 4 x 4 in.; the support for the needle maybe made of woodor glass tubing ; and the needle itself a piece of magnetizedknitting-ne
. Laboratory exercises in elementary physics. 18 uncovered copper wireruns up from binding-post a, and to it are attached the ends ofthe naked iron and copper wire, as indicated. The number oflengths of these depends upon the size of wires. For the slidingcontact, the end of a piece of No. 18 copper wire may be ham-mered out flat, and then bent into the form of a hook. An Eng-lish binding-post is best. Sensitive Galvanometer. (See Fig. 115.)—The frame is of woodabout 4 x 4 in.; the support for the needle maybe made of woodor glass tubing ; 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 APPENDIX C. one inch apart and the lower one only should be magnetized. Theframe is wound with wire as shown by the dotted lines, with asmany turns as desired. Space is left in the middle to admit the. 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 serves toshow the motion to a class. If this were used, the indicating-needle would not be needed. The whole may be covered with abell-jar, or a large glass bottle whose bottom has been cut off. Coils of Wire.—These are made of cotton-insulated wiremeasured off in the lengths indicated in Exercise 4, wound intoa coil on two fingers and attached to a piece of stiff card-board by CONSTRUCTION OF APPARATUS. 233 paper-fasteners or wire passing through holes in the card andaround the coil. The number and length of the wire are markedon the card, which may then be shellaced to preserve it. Theends of the coils are left free for two or three in., and the
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Keywords: ., bookcentury1800, bookdecade1890, bookpublishe, booksubjectphysics
