APPARATUS FOR STATIC ELECTRICITY.
_236. Static or Frictional Electricity._ There are many interesting and
instructive experiments in this branch of electricity. All that can be
done here is to explain a few pieces of simple apparatus to show the
presence of static electricity, it being taken for granted that you know
how to produce it, and that you have some book of simple experiments.
_237. Electroscopes_ are instruments for showing the presence of static
electricity.
APPARATUS 134.
_238. Thread Electroscope._ A piece of ordinary thread may be used for
this purpose. Tie one end of it to the back of a chair or other support.
APPARATUS 135.
_239. Pith-Ball Electroscope._ Fig. 107. The pith from elder,
corn-stalk, milk-weed, etc., is very light and porous. When this is tied
to the end of a silk thread, we get the pith-ball electroscope, so much
talked about in nearly every text-book on physics. The upper end of the
thread may be tied to any suitable support. Fig. 117 shows a book, lead
pencil, and a small weight to hold the pencil steady. The thread is tied
to one end of the pencil.
[Illustration: Fig. 107.]
APPARATUS 136.
_240. Support for Electroscopes, etc._ Fig. 108. Glue or nail a spool,
S, to a wooden base, B, measuring about 4 x 5 in. Wrap some paper
around a 7 in. length of 1/4 in. dowel, D, to make it fit the hole in S.
Wind one end of a wire, W, around the top end of D. To the outer end of
W tie a silk thread, S T, on the lower end of which may be tied a piece
of pith or material to serve as an electroscope.
[Illustration: Fig. 108.]
APPARATUS 137.
_241. Carbon Electroscope._ Carbon will be found to make a most
excellent electroscope, as it is light and a good conductor of
electricity. Light an ordinary match and let it burn until it is charred
through and through. The black substance remaining is carbon. Tie a
small piece of the carbon, about 1/4 in. long, to one end of a silk
thread, and support the thread as in Fig. 107 or 108.
APPARATUS 138.
_242. Pivoted Electroscope._ Fig. 109 and 110. Fold a piece of stiff
paper double, then cut it into the shape shown. It should be about 3 in.
long and 1 in. wide when opened out. A hole, B, about 1/2 in. in
diameter should be cut in it while folded. A piece of paper, C, should
be pasted to A, so that its top, where it is creased, will be about 1/8
in. above the top of A. The support consists of a pin, E, stuck through
a cork, D. Balance the paper on the pin, which passes up through the
hole, B. An electrified body brought near this apparatus will make it
whirl around very decidedly.
[Illustration: Fig. 109.]
[Illustration: Fig. 110.]
APPARATUS 139.
_243. Fancy Electroscope._ Fig. 111. Fold a piece of stiff paper double,
then cut out some fancy-shaped figure, as suggested, and draw the face,
clothes, etc., to suit. This being folded through the center for
cutting, it can be balanced upon a pin-point as explained in App. 138.
[Illustration: Fig. 111.]
[Illustration: Fig. 112.]
APPARATUS 140.
_244. Box-Cover Electroscope._ Fig. 112. A pasteboard box-cover,
balanced upon a pin, makes a fairly good electroscope, although it is
not nearly so sensitive as App. 138. The pin may be stuck in the upper
end of the dowel, D, shown in Fig. 108.
APPARATUS 141.
_245. Leaf Electroscope._ Fig. 113. This is a very sensitive instrument,
and can be used to tell the kind of static electricity on a body, as
well as the mere presence of it. (See experiments in text-book.) The
lamp chimney acts as a support for the leaves, L, and it protects them
from currents of air. A tin box-cover, C, has a small hole punched
through its center. Through this is pushed one end of a wire, W. This
may be a hairpin, straightened. The upper end is bent over at right
angles, after passing it through the hole. The lower end is bent as
shown. On this horizontal part is fastened the leaf. These should be
made of aluminum leaf, or of Dutch metal. The former will stand more
rough handling than the latter. Goldleaf is used for very sensitive
instruments. It is a little too delicate for unskilled hands.
[Illustration: Fig. 113.]
[Illustration: Fig. 114.]
246. To cut the aluminum leaf, place it between two pieces of paper,
then cut paper and all into the desired shape. The piece should be about
3 in. long and 1 in. wide. Fold this across the middle, and stick it to
the underside of the wire (Fig. 113). Saliva will make it adhere to the
wire, if you have nothing better.
APPARATUS 142.
_247. To Show Where a Charge of Static Electricity Resides._ Fig. 114.
This shows a tin baking-powder box placed upon a hot tumbler. A moist
cotton thread is hung over the edge of the box. (See experiments in
text-book.) The box will become charged by touching it with a charged
body. The thread will show whether the charge resides upon the inside or
upon the outside of the box.
APPARATUS 143.
[Illustration: Fig. 115.]
_248. Support for Electrified Combs._ Fig. 115. In the study of static
electricity, ordinary ebonite combs can be used to great advantage. A
bent hairpin will serve as a cradle to support them. A silk thread may
be tied to the wire, but a narrow silk ribbon is better than thread, as
it will hold the comb steady.