Los Angeles herald., 1908-03-01

The earth is like a great magnet, and be
cause of the attraction between particular
ends of two magnets, one end of the compass
will always point nearly noAth =,
Take q common compass or other small
magnet, and hold wire carrying current
horizontally over it, and you will hnd that
the needle viii turn at right angles to the
wire
wire, facing the magnet, with the current
entering his head and going out at his ieet,
the end of the magnet that is at his right
hand will be the end that will point to the
north In horseshoe magnet 1t generaiiy mas
q scratch like this on it.
Opposite poles of magnets attract each
other. Thus, the north, or = pole, or end
of one will attract the south or pole OF an.
other. This principle, and the fact that SOFT
iron is magnet only while the cuffent Is
passing, are used In the construction Oh sinpie
Now, few words about batteries. Here
we come to the meaning of the positive or
negative, or r and ends OF currenS;
battery works by chemical action. There
are two principal substances in it called
plates, these substances being different, ac-
cording 10 the kind of battery. -,
We will take, for example, the Danieils
volt Of current. Take glass jar of suitable
size and porous jar much smaller In dame.
ter, but Just as high. Put large piece OF
sheet copper in solution Of copper sulphate
(blue yitriol, or blue stone) IN the glass jar,
and piece of zinc in dilute sulphuric acid,
or in a solution of zinc sulphate twhite Wit
riol). in the porous cup.
Another form of this battery is ordinarily
used in telegraph Offices. The, chemical ac-
ton is greater on the zinc, and current IL
per. Ii you fasten piece of wire from the
copper to the zinc, the current will pass
along the wire back to the zinc. If you put
some electrical apparatus, between the tive
plates, the motor, or whatever it is, VIII
work, if the battery is strong enough.
Now observe that within the battery the
current flows from the zinc to the copper,
but outside the battery from the copper to
the zinc.
The copper and zinc are called plates, and
called electrodes. Thus you see that the
zinc is the positive or r plate, and carries
the negative or electrode, while the cop
per is the negative plate, and carries the posi-
tive .electrode. The current alawys flows from
positive to negative, or + to
Suppose you have several of these bat
teries. To connect them in series, you must
join the copper of one to the zinc of the
next, the copper of that to the zinc of the
third, and so on; and then the line wire goes
from the copper OF the last to the zinc OF the
first.
But if you want To join them parallel, you
connect all the coppers together and all the
zines together, and run your line wire from
anywhere on the copper connection to any.
where on the zinc connection.
The +. M. +. of any given kind of battery
does not vary, no matter how large or small
il is; but a battery has resistance the same
as wire, and large battery has less resist
ance than a small one.
If you take two batteries and join them in
series, the E. M. F. of the two will be twice
the f. NJ f. of either, and the resistance win
also be doubled. But if you join them paral-
lei, the e. NJ +. of the two viii be the same
as that of only one, while the resistance-as
in the case OF wires-will only be one-half
that of one. 1t is, in fact, as though you
had one large battery.
In applying Ohm's law, you must count in
the battery resistance as well as that of the
wires.
The principles that I have given you here
will enable you, with little thought, to do
any simple electric work on your own &C.
count.