Evening star., 1896-12-05

around as line needle, and is technically
known as No. 3d. John bought all he need
ed of this wire at an electrical supply store
icr h1teen cents. The winding of the wire
had 10 De done with great care, and II any
young reader tries Johns experiment for
himself he should follow these directions.
Hold one end of the wire in the left hand,
ieaVihg couple of inches free With the
right hand wind. as evenly as possible,
parallel with the shaft. 1t is not necessary
that the wire should cover the whole sur
lace of the core but rather that there
should be bunch, SO to speak-coyering
ahout one-quarter of the core on either
SIDE; A clear idea of the way this should
De done can be had from the picture of the
a1mature. Enough LAYERS should he u,onna
10 make the punches project from the core
aoout NTH of an inch. When the last
,a ,sSer IS on the free end of the wire should
oe prougnt TO the same end of the armature
ccre as the wire underneath.
Alter tn;s was done John took q strin of
cotton batting and wrapped 1t twice around
the ions oi,s eiu OF the armature shaft close to
.le core In such a way as to bind the
under WIRE to the shaft. Then he hound a
strip OF thin sheet "copper" one quarter of
an inch wide, around the cotton. making
ths aii ,,ah nole IN the copper. through which
me me INBOUND wire was passed and fastened.
Inen ne repeated the cotton winding and
copper binding operation at a point a nuar
yer OF an inch nearer the end of the shaft.
fastening the free wire exactly as he had
done with the other wire and conner The
copper was borght for a few cents from an
electrical supply store, the same as the
wire mad been. and when that was done
tne armature was all ready to be put in
place Having attended to that. John look
small spool on which silk had been
wound and slipped 1t on the end of the
smart which projected from the frame
RMS spooi was later to serve as the "pul-
ley by which the shaft was revolyed.
Making the Current.
The dynamo was then completed by cut
Strtr -
and quarter inches long and a quarter
of an inch wide. and inserting them
through the oblong holes that had been
made in one Of the projecting arms of the
frame, in such way that the free ends of
the copper rested on the copper bands out
side the cotton batting that was wound on
the shaft. These fiat pieces Of copper an
SWered to the brushes and the copper
bands to the ''exciters' of a regulation dy-
namo. When the armature, which, after
being wound is just large enough to Craze
the upper and lower parts of the magnet, is
generated and conveyed through the wire
and exciters to the brushes.
II short piece of wire were made to
connect the ends Of the brushes that pro-
ject through the arm, this current Of cleo
tricity " Would pass from the armature to
enc brush. through the wire and directly
back to the other brush and thence to the
armature again. thus forming a complete
circuit. If the wire Is longer the current
has TO travel farther, and IT, before It re-
eurns to the dynamo, 1t is passed through
a lamp the lamp will glow, and that is the
way all electric lighting is done Johns
dynamo would not furnish enough current
to light even an ordinary sixteen-candle in
candescent lamp, but there was enough of
1t TO make one of the little pea lamps"
which John bought at an electrical Supply
store for 50 cents, glow with dazzling
brightness. In the picture John is shown
holding this little lamp In his hand
Power From a Sewing Machine.
When he first started the dynamo to
running, he got his power from the big
wheel of his mothers sewing machine,
and his younger brother sat and worked
the pedals for him. OF course, the faster
he made tie wheel fly, the more electricity
was got from the. dynamo. and the wheel
Of the sewing machine had to be worked
very fast In order to make the lamp glow.
The dynamo made what IL know as an
alternating current-that is, the current was
produced only when the two punches of wire
passed the magnet For this reason when the
revolutions were slow the lamp would glow
for an instant and then be dark for an
instant, but when the armature was made
fairly to buzz the glow would be steady
a.HS 1t was not not cas-, easy to ksep up the power
Ing machine wheel and 1t was not very
long before John fixed up a system OF
c1ockwork with a heavy weight, which,
Wnen WOUND, would run the Dynamo Tor
a long time. He had an Interesting ex-
perience very soon after his little machine
was completed. He forgot that electricity
always seeks the easiest road and he held
the two wires in his hand In suoh q way
as to receive the current through his body.
OF course, 1t was not strong enough to
injure him, but 1t startled him and made
him understand better than he ever did
before how the accidents happen around
dynamos, SO often reported in the news
papers. If John had placed small motor
so that the current would pass through 1t
as 1t did through the little pea lamp, the
motor would have whirled exactly as large
motors connected with large dynamos do.
And, as a matter of fact, John did after
ward construct a small motor under the
direction of his electrical friend, and found
II much simpler task than the making of
the dynamo itself.