Evening star. [volume] (Washington, D.C.) 1854-1972, 1913-02-20

In no other way is the progress of sci
ence brought home more strikingly than
| in the development of our knowledge of
| invisible light Not only has the sci
enlist discovered rays of light which the
| human eye has never seen and can never
| see, but he has found how to use that
| knowledge for the benefit Of our every
day life. He has found rays of light so
weak that ordinary glass, however trans
| parent to the vision, shuts it out effect
lively, and yet they are so strong that
| billions of germs may be killed merely
by coming within the scope of their in
fiuence. From the dawn of creation to
the recent past they have shed their in
| fiuence upon men, yet men have been
| wholly unconscious of their existence. In
| the few short Years that have gone by
| since their discovery we have demon
strated that even in the inkiest of dark
| ness there may be brilliant lights.
Such a paradox could not be believed
by the ordinary layman did not the eye
OF the camera reveal its truth. That in
struEent shows us that the eye is senSi-
tive to only very small proportion of
the total radiation that reaches it. dis
covery that leads the scientist to believe
mat If the eye could recognize all this
radiation it would reveal a thousand
wonders undreamed Of Gradually the
scientist is developing refined instruments
which are capable OF detecting what the
human eye cannot perceive and it is be-
lieved that many new things will ulti-
mately be learned through them
Dr. Il. w Wood. professor of expert
mental physics at Johns Hopkins Univer-
Sity, is one of the world s authorities upon
invisible light. and he illustrates some of
the remarkable things about invisible
ilShl- + or instance. he says that if the
finger be dipped into zinc oxide and
ruDoed over white sheet of paper the
eve Will be unable to detect the presence
or the streaks OF the white powder I'M
less II mas been Veryth!ckly applied. IF.
however, that piece of paper be pho.o-
graphed with ultraviolet light it appears
to be marked with streaks of charcoal
rms experiment led 10 the deduction that
II the moon and planets De photographed
with invisible light. substances which do
not appear usually might be brought out
:: :;
In a demonstration of this theory DR.
Wood had constructed a sixteen-inch
mirror OF
Special Mirrors Used twenty
in Making Photographs. s,S ns
coated with nickel. which is used in
combination with a plate of the new
ultraviolet glass. heavily silvered. The
region around Aristarchus, one of the
craters of the moon, was photogra pied
with yellow and then with ultraviolet
light. Then two specimens of volcanic
tuff were photographed in similar way.
1t was found that the one sample when
photographed with ultraviolet light cor
responded identically with the deposit
surrounding the crater Aristarchus. 1t
was analyzed and found to contain iron
of SlIln
rocks were coated with iron oxide and
they We're photographed with the ultra
violet rays. but the iron showed none
of the peculiarities of Aristarcilus when
SO photographed. After this an invisible
coating of sulphur was formed on "a
piece of light gray rock by the applica-
ton of a fine jet. When it was photo
graphed with the invisible rays it was
black-exactly like the crater of Aris-
tarchus. From this Dr. Wood was able |
to infer that this spot on the moon is al
extensive deposit of sulphur. resulting
from vapor elected from the crater
In explaining the mysteries of invisible |
light before the Royal Institution of
Great Britain DR.. Wood took two pieces |
of scarlet silk which could not be dis |
tinguished under an incandescent light |
and placed them under a Cooper Hewett |
mercury arc lamp, with the result that |
one CUHtlllue0 10 appear scarlet, Wnlle i
the other appeared almost black. The |
mercury lamp gives off almost no red |
rays, consequently red objects appear
almost black. But the other piece of silk |
was colored with a dye that became flu |
crescent under the green light of the |
mercury lamp.
DR.. Wood and Prof Rubens de-
vised sort OF ray filter. with which |
they could separate the visible from the |
invisible rays of light, and with it they |
We're able to isolate the longest heat |
wave ever discovered. 1t consists of a |
box in which is imprisoned an electric |
spark. The ultraviolet rays of light |
from ii brought to- focus upon a |
small circular aperture upon card |
board screen. and the focal length of the |
lens is made great that the visible |
rays cannot come to focus at all. Held |
before the light white paper was black |
but when uranium nitrate crystals were |
substituted the presence of the ultra |
violet rays was made manifest by the |
crystals shining with a brilliant green |
light.
Metallic mercury vapor shines with |
brilliant light when exposed to the in |
visible ultra |