Part 5 (1/2)

APPARATUS 51.

_69. Binding-Post._ Fig. 35. The ends of two or more wires may be quickly joined electrically by placing them between the nuts of a short bolt. By using 3 nuts the bolt will more easily connect a large number of wires.

[Ill.u.s.tration: Fig. 35.]

_Make Additional Notes and Sketches Here._

CHAPTER VI.

PERMANENT MAGNETS.

_70. Permanent Magnets_ may be made in many ways and from many different kinds of steel. The steel used for needles, watch and clock springs, files, cutting tools, etc., is generally of good quality, and it is already hard enough to retain magnetism. (See Retentivity in text-book.)

APPARATUS 52.

_71. Bar Magnet._ A straight magnet is called a bar magnet. Magnetize a sewing-needle. For some experiments a needle-magnet, as we may call it, is better than a large magnet.

APPARATUS 53.

_72. Bar Magnet._ A harness-needle, which is thicker and stronger than a sewing-needle, makes an excellent bar magnet.

APPARATUS 54.

_73. Bar Magnet._ For long slim magnets use a knitting-needle. Some knitting-pins, as they are sometimes called, break off short when bent, but most of them will bend considerably before breaking. These slim magnets are excellent for the study of Consequent Poles. (See text-book.)

APPARATUS 55.

_74. Flexible Bar Magnets._ It is often necessary to have flexible magnets so that they may be bent into different shapes. These may be made from watch or clock springs, as such steel, called spring steel, will straighten out again as soon as the pressure is removed from it.

Corset steels, dress steels, hack-saw blades, etc., make good thin flexible bar magnets.

APPARATUS 56.

_75. Strong Bar Magnets_ may be made from flat files. The handle end may be broken off so that the two ends of the file shall be nearly alike in size. These should be magnetized upon an electro-magnet.

APPARATUS 57.

_76. Compound Bar Magnets_ are made by first magnetizing several thin pieces of steel, and then riveting them together so that their like poles shall be together, and pull together. To make a small compound bar magnet, magnetize several harness-needles, or even sewing-needles, and then bind them into a little bundle with all the N poles at the same end. Melted paraffine dropped in between them will hold them together.

Rubber bands may be used also, or, if but one end is to be experimented with, the points may be stuck into a cork, and the heads used to do the lifting.

APPARATUS 58.