Saint Mary's beacon. [volume] (Leonard Town, Md.) 1867-1983, 1897-04-08

Tnis IL what Happens when tina Ars
Light Il Burning.

Light Il Burning.
The electric arc light, with its in
tense, steady brilliancy. Is now SO
familiar an object that few stop to
think how wonderful q thing it
really is. Here is light enough to
illumine many square yards nearly
as well as daylight does. proceeding
from the points of two little carbon
rods as large as ones finger. What
is the state of the carbon in that
small spot? Professor S. p. Thomp-
son, in a recent Cantor lecture be-
fore the Society of Arts in London,
tells Us that it has actually melted
there, something that was until re-
Gently thought impossible. More
over, he says that when the light
misses, the liquid carbon is really
boiling. The facts that lead him to
these conclusions are quoted below
from the report of his lecture that
appears in Industries and Iron:
Captain Abney had found the
white surface of the luminous crater
to be always of an equal degree of
whiteness, which obviously means
that it is always of an equal degree
of temperature. The only thing that
could account for there being fixed
temperature for the crater surface
was the fact that carbon is at the
surface in a state of volatilization !;
that tho carbon is evaporating off
from the positive carbon into the
arc or fame. At that surface you
necessarily must have the tempera-
ture at which carbon evaporates,
just as you cannot have the surface
of ice under ordinary conditions
either hotter or colder than the tenn
perature which is taken as zero of
the Centigrade scale. My present
view of the physical state of the arc
crater is that the solid carbon below
is covered with q layer or film of
liquid carbon, just boiling or evap-
Grating off.
when kissing takes place, a new
state of things is set up. If you
watch a short, kissing arc, you will
see a column of light concentrating
itself on q narrow spot, and the spot
keeps moving about and is very un-
stable in position as well as in the
amount of light it gives out. The
contracted spot from which light
seems to start pits deeper into the
carbon. Mrs. Ayrton made the OBJ
servation that the crater surface,
after the arc has been kissing. is
found to be literally honeycombed.
When the arc is kissing, you can see
little bits erupted out, and the hiss.
ing seems to be comparable to the
kissing which takes place in water
Just when it is beginning to boil. II
you have some water being heated
in such a way that there is not more
than q certain quantity of heat Civ.
en- off from the surface, you have
the water evaporating quietly, but
you cannot get more than q certain
quantity of heat given off PEI
square inch of top surface OF the
water in that quiet way.
If you force more than a Ger.
tain quantity of heat to pass of
per top square inch of the water,
you find the water begins to breal
up internally, and you have bubble:
formed below the surface; the sur
face breaks up, the bubbles are
thrown out, and you have a noisy
phenomenon. think you will find
there is exactly the same kind OF
difference between the silent arc and
the kissing arc as between quiet
evaporation and noisy boiling.
There is n sort of decrepitation, a:
the solid particles are being tori
asunder to make way for something
coming out, when tho arc is hiss.
ing. Literary Digest.