88 
THE YOUNG SCIENTIST. 
plates, and on the proper degree of thick- 
ness which they ought to have in order to 
give tlie best results. 
How to Make an Electric Bell. 
FIEST, obtain at the blacksmiths' a 
piece of round iron about four and a 
half inches long and of a size that will fit 
the hole in a thread spool about an inch 
and a quarter long. Have the iron bent 
into a U shape as in Fig. 1, the arms of 
which should be about one inch and a 
quarter long and one inch and a half 
apart. Take the spools and whittle them 
down to a thin shell, so as to allow the 
wire w^hich is to be wound around them 
to come as near the hole as possible. 
Divide your insulated wire into two equal 
lengths, each of which is to be wound 
around the spools separately. Before 
beginning to wind the spools drill a small 
hole the size of the wire through the 
wooden shell at one end, then insert one 
end of the wire, letting it project a few 
inches from the inside, then begin to wind 
the first layer, and wind neatly back and 
forth until all of that piece of wire is used. 
Wind the other spool in the same way, 
taking care to wind both spools in the 
same direction. After this is done place 
the spools on the arms of the U ; scrape 
the insulating covering from the ends of 
the wires which were left projecting from 
the inside of the spools, and twist them 
together as in Fig. 2. This U-shaped iron 
with its spools of wire, will, when pro- 
perly connected with the poles of the 
battery, form an electro-magnet, the iron 
being magnetic only when the coils of 
wire around it form the circuit of a 
battery. 
To make the armature and bell-ham- 
mer : Take a strip of iron one inch and 
three-quarters long and about as thick as 
a ten cent piece and rivet to one end of 
this piece of iron a piece of clock-spring 
about one inch long. To the other end 
solder a stout piece of wire the size of a 
knitting-needle, four inches long, and 
fasten to the end of it a small knob, ^fter 
which bend it into the shape shown in 
Fig. 3, which shows the armature and 
bell-hammer complete. To make the 
circuit-breaker: Take another piece of 
clock-spring an inch and a quarter long 
and punch a small hole in one end, into 
which rivet a short piece of copper wire 
which may afterwards be filed down to a 
small knob on the spring. Solder the 
other end of the spring under the head of 
a round-headed brass screw, as in Fig. 4. 
Next procure the bell. Any bell not 
exceeding six inches in diameter will 
answer. 
To put the apparatus together and 
operate : Obtain a board about one inch 
thick, four inches wide and nine inches 
long. Screw the electro-magnet to the 
board as in Fig. 5 by a small cross-piece. 
Support the armature close to and op- 
posite the ends of the electro-magnet by 
fastening the end of the spring to a small 
brass support shown at a. Screw the 
circuit-breaker. Fig. 4, into place at b, and 
bend it so that the little knob will just 
touch the stout wire where it is soldered 
to the armature. Screw the bell on at f, 
so that the knob will just strike the edge 
when the armature strikes the ends of the 
magnet. Paste a small strip of thin paper 
on the inside of the armature so it will 
not stick to the ends of the magnet, as the 
particles of steel in the iron do not lose 
their magnetism when the circuit is 
broken. Bememher that all contacts of 
wires and other parts through ivhich the 
current is to flow must be scraped bright. 
When all parts are in place, connect the 
wires as follows: one wire from the 
electro-magnet is to be led to and placed 
between two copper washers which are 
clamped together by a round-head screw, 
screwed into the board at d. Fasten the 
other wire from the magnet to the sup- 
port which holds the armature at a. Then 
with a short bit of copper wire connect 
the screw which holds the circuit breaker 
with two more copper washers arranged 
to clamp the wire at e in the same way as 
at D. To ring the bell, clamp the wire 
from the positive pole of the battery, 
between the washers at d. Then with the 
wire from the other pole touch the 
washers at e, and if the apparatus has 
been properly made and adjusted the bell 
will ring while the connection is made. 
Now trace the course of the current. It 
