TUS 66.

_87. Compass._ Fig. 41. It is an advantage to have a magnetic needle
that is always ready for use. The support is made by driving a pin
through the top of a wooden pill-box, which should be about 1-3/4 in. in
diameter. This gives plenty of room under and around the needle. If the
pin be left too long, it will not be possible to put the bottom and top
of the box together when you want to put the compass away. Cut the pin
off (App. 35) at the right length, so that the magnetic needle can be
safely put away in the closed pill-box.

88. The "Needle," that is the short bar magnet, may be made of
watch-spring. As the spring is already quite hard and brittle, it may be
easily broken into desired lengths. It is always better to make 3 or 4
needles at a time, as some will swing more easily than others, and time
will be saved in making them. Break off 3 or 4 pieces of thin spring,
each about 1-1/2 in. long. Bend them as in Fig. 42. A good dent, not a
hole, should be made at the center of each to keep them upon the support
or pin-point. A "center punch," not too sharp, is the best tool to use,
but a slight dent may be made with a sharp wire nail, provided the
watch-spring is first annealed or softened. (See App. 21.) Do not place
the spring directly upon iron or steel when making the dent, as these
might injure the point of the punch, and the dent would not be deep
enough. Fig. 42 shows a good way to make dents in steel springs. Place 2
or 3 layers of copper or lead between the anvil and the spring. A hammer
or hatchet will do for the anvil. As the copper will give easily, a good
dent may be made by striking the punch or nail with a hammer. If the
spring has been annealed before denting it, it should be hardened again
(App. 21) before magnetizing it, so that it will retain magnetism well.
(See Residual Magnetism in text-book.)

[Illustration: Fig. 42.]

89. Balancing. After a dent has been made, place the spring upon its
support so that the pin-point shall be in the dent. It will, no doubt,
need balancing. If one end is but slightly heavier than the other, the
spring may be balanced by magnetizing it so that the lighter end shall
become a north pole. This will then tend to "dip" and make the needle
swing horizontally. If one end is much heavier than the other, it should
first be magnetized and then balanced by cutting little pieces from the
heavier end with tinners' shears, or by weighting the lighter end with
thread,