Juniata sentinel and Republican. [volume] (Mifflintown, Juniata County, Pa.) 1873-1955, 1883-04-18
Physics which Apparatus

During lecture course Dy professors
who have at their disposal complete
set of physical apparatus, there are
some experiments performed by them
which at first sight seem very complicat'
ed bur which nevertheless may be re-
peated by means of very simple objects.
( There is, for instance, the interesting
Lissaiols experiment. which consists,
as the reader Is perhaps aware, IN throw
ing on A screen, by means OF the oxyhy'
drogen lamp. the curves traced by one
of the arms of tuning fork in sonor.
Gus vibration. An analogous expert
ment nay be exhibited by means OF a
common knitting needle. FIX one OF the
extremities of the needle in a cork to
serve as base; then to the upper free
extremity attach bali of sealing wax,
and ON this gum small circle OF paper
about the diameter of pea, Now.
holding the cork firmly between the
finger of the left hand, cause the needle
to sharply vibrate, either by bending 1t
far to one side and then suddenly releas-
ing 1t, or by striking it smartly with a
wooden ruler. The little ball of wax
surmounted by paper will be seen to des-
cribe a moreior less elongated eiiipse, or
a circle, according to the intensity or
the number OF vibrations. The phenom-
enon Is very perceptible when care Is
taken to cause the needle 10 vlbrate
urder a strong light from a lamp; and,
in such case the persistence of the IN
preston on the retIna causes the ylbra-
ling wire to form an image which has
the appearance of long and graceful
bouquet holder, or champagne glass.
Among the experiments sometimes
performed to demonstrate molecular at
fractions, there is one which is execut-
ed by means of an apparatus OF pecul-
lar structure but the same phenomenon
may be shown Ill a much more simple
manner, as follows: Having cut two small
spheres ont of bottle cork, place them
ON the surface of water. Ii one of the
balls now be carefully pushed along un-
I'll it Is In quite close proximity to the
other, the two will be seen to quickly
rush towards each other, Just as bit oi
iron flies to a magnet when the latter Is
brought near 1t.
A writer has pointed out a neat meth
cd OF obtaining an electric spark by
means of simple apparatus which he
calls the ''tea-tray electrophorus. A
common metallic tea-tray Is supported
Ell two dry glass goblets. A piece OF
common brown paper, cut SO as to be a
little smaller than the tray, and with
round corners is warmed, lard on the
table and rubbed briskly with a piece
of Indla-rubper, or with a clothes brush
1t is then laid down for an instant on
the tray. Ii at this juncture some per-
son presents his knuckle to the tray he
will receive a bright spark, which under
favorable circumstances may be couple
OF inches loBg. BY simply putting the
paper down, touching the tray, and
again lifting up the paper, the tray If
again charged, and large humber OF
sparks may be thus drawn one alter the
other In rapid succession. The paper
may be lifted by the hands. but 1t will
be found better If couple OF strips oi
paper be fixed on with wax 10 serve as
handles
The sparks obtained by the tea-tray
electrophorus may produce shghi
pricking sensation, but to give regular
electric shock will oblige us to store VI
charge in Leyden jar. This import.
ant piece OF apparatus may be lmprovis
ed as follows: 4 round bottomed glass
tumbler is procured-thin glass Is pre-
ferable-and is filed about three quart
ers full OF small leaden shot. LII shot Il
not at hand dry coal dust will answer,
though not so well, and great care mus
be taken to wipe clean the upper part o.
the tumbler, Everything must be warn
and scrupulously dry. Into the shot Ii
inserted a silver spoon to serve the
place OF a rod and knob. The tumblel
Is held by graspng 1t well in the bottom
OF the haed. SO that the palm may coyel
fthe whole of the rounded bottom. Hay
ing thus prepared and grasped the I'M
provised Leyden Jar, it Is to be charget
with sparks from the tea tray electrop-
horus. 1t should be held with the
spoon handle near to, but not touching
the edge of the tea tray, while anothel
person performs the operations OF Lifting
the paper up and putting 1t down, thel
touching the tray. then lifting up agail
and so on until a dozen sparks hay
been sent into the jar. On touchin,
the '.knob" smart little shock Is ex
perienced In the wrists aud elbows, an'
short, bright, Swapping spark announ
ces the discharge OF the jar.
|