If a piece of paper is then heated over a lamp or stove and rubbed
with a piece of cloth or a small broom, the arrow will turn when
the paper is brought near it.
--Contributed by Wm. W. Grant, Halifax, N. S., Canada.
** Miniature Electric Lighting [104]
Producing electric light by means of small bulbs that give from
one-half to six candle power, and a suitable source of power, is
something that will interest the average American boy.
These circular bulbs range from 1/4 to 2 in. in diameter, and cost
27 cents
[Illustration: FIG. 1]
each complete with base. They are commonly known as miniature
battery bulbs, since a battery is the most popular source of
power. The 1/2-cp. bulbs are usually 2-1/2 volts and take 1/4
ampere of current. It requires about three medium dry cells to
operate it. However, there is now upon the market a battery
consisting of 3 small dry cells connected in series, put up in a
neat case with 2 binding posts, which sells for 25 cents. This is
more economical than dry cells, as it gives about 4 volts and 3
amperes. It will run as large a lamp a 3-1/2 volts, 1 cp.
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