Evening star. [volume] (Washington, D.C.) 1854-1972, 1911-02-19

and 1mpat1ently pushed aside the power
full microscope and the delicate bolometer.
1t is most discouraging, " he muttered, to
have such treasure before ones eyes and
still be unable to grasp it,!
looked in the little box, surprised to find
nothing but few brilliant firef1ies. The
scientist began to explain.
"In that box is the most efficient illumi-
nant known to man. The radiant output
from one of those insects corresponds to
nearly fifty watts a candle, while our very
best artificial illuminant, the flaming arc
lamp, gives only two or three watts to the
candle. The light from those insects, as re-
corded by the bolometer, radiates little if
any heat, while the very best incandescent
lamps waste more than ninety per cent. of
the electrical energy in useless heat. If |
could read this secret of the insect world and
make a lamp after its pattern, | could pro-
duce three hundred and eighty-four candle
power from the same current that gives six
teen candlepower to-day. Some day the
secret will be read. y
Light and electricity travel at nearly the
same speed, one hundred and eighty-six
thousand miles second Even at this enor-
nous speed there are instruments delicate
enough to measure it. The source of all light
Except the light from firef1ies and their king
is substance raised to a temperature sui
flclent to set up waves IN the surrounding
ether, which, when falling upon the eye, pro-
duce the sensation we know as light. Light
waves vary in length between one thirty
three thousand four-hundredth and one
sixty-five-t housandth of an inch; the first
being extreme red and the second extreme
violet. Rays of white light have length of
one forty -fve- thousandth of an inch The
sun is a great mass of white hot matter. 1t
-. xl,1A ii
light, and outside of Our atmosphere it is alb
solute darkness, as dark as the interior of
Mammoth Cave In an arc lamp it is the
white hot particles of carbon floating be-
tween the two electrodes that produce light.
In the incandescent lamp it is the hairpin
filament inside the glass globe that, when
heated by electricity, gives off light waves.
In gas and oil lamps light is produced by the
heated particles of carbon in the flame above
the wick or mantle.
The eye can stand, without firing, bril-
lance of about five candlepower to the square
inch of surface. The ordinary candle flame
gives only two or three candlepower to
the square inch, while the sun at zenith gives
six hundred thousand The arc light ranks
next to sunlight, with ten thousand candle
power an inch, and the best tungsten fila
ment incandescents give one thousand
IIlo IliStiilo Iide IL IiiS oliiA
could be changed into ball of tungsten it
would throw off only one thousand candle
power of light from every square inch of its
surface, when the world would be practically
dark, and we should freeze to death in a
week.
The prism shows that white light is COM
posed of happy blend of all colors of the
spectrum. The sun gives the only pure
white light, with the arc lamps close
second, and the metal flament incandes-
cents taking third place. Skylight, such as
comes from the north on clear day, IS
blush white. Gas mantles give greenish
light, open fame yellow light, and kerosene
orange light.
| No Color In the Dark
IN the dark there is no such thing as
! color. The reddest dress is just the same
color as pure white tablecloth when both
are placed in a dark closet.
| If you would understand this, assume the
presence of a light wave motion in the ether.
| The color of light depends upon the length
of these waves. The light waves producing
the colors in the blue end of the spectrum are
very short compared with those that pro-
duce the colors near the red end. The light
source that we know as red gives off only
waves of a length to produce that particular
color. A body appears red because its SUR
face absorbs all the other waves and reflects
Il 81, I<o1 s~,@o Of