National Republican. (Washington City (D.C.)) 1872-1888, 1875-01-08
FLUORESCENCE.
PROF. HENRY MoRTON'S SECOND
LECTURE.

LEW ONGs
DEFINITION OF TERMs-BRILLIANT EX-
ACKNOWLEDGEMENTS OF FLUoR-
EsCENCE-THE INVISIBLE SPECTRUM
APPLICATIONS OF FLUoREsCENCE-DIs-
. CoyFRY OF NEUTRALITY-SUSPICIOUS. EX-
PLANTATION OF FLCOREsCEHCE-
DESPITE the terribly Indictment weather last
evening Lincoln hall was we'll flied and by IN
audience keen for instruction, to hear the second
lecture OF Prof. Henry Norton His subject
huoresceece-was made intensely interesting by
the thorough scientific knowledge Of the lecturer
and by a series Of brilliant illustrations, which
served as q guide in the journey with him to zone
Of the inaccessible uplands Of science" After ex
planning how fiuorescence is . changein the wave
length or color OF light rays he reviewed the re-
lations OF ordinary eolored objects to the light
waves, and in the following synopsis the scope Of
inquiry and the nature Of the ground gone over
Wal be seen:
When beam Of pure white light is passed
through prism or is anslyzed, as we call It, We
get the well-known series Of colors, red, orange,
yellow, green, blue, indigo, violet. Beyond the
violet however, there are Invisible rays for dis
tanee moro than Ave times as great as the length
Tays and produce Photographic and chemical
effects. The lecturer exhibited drawing Of the
invisible spectrum by casting on screen the
greatly magnlned image Of Fig. 2
Although the difference between the colors
seems but slight, only difference in the length
OF the wave, yet each element Of the most COM
posite beam Of light is so unalterable that the
least change Of tint never takes place. Red
light, though 1t were passed through hundred
lenses or prisms, cannot become one atom more
less red, and still less can It be changed to
other color.
not white light changed to green when it falls
upon Leaf or to red when 1t strikes brick
wall? No; white light contains all eOlOrs; when
1t falls on q leaf all rays OF light except those
producing green are absorbed by the leaf or con-
Yerted into other forms OF force while only the
green are reflected. On the other hand, red OBJ
iects absorb all but the red rays. To prove this
q cluster Of banners of various bright eolOrs was
illuminated successfully by light Of different
tinis. The banner having the same color as the
light remained bright, while all the others sp-
poared black. If colOred objects changed the
color Of the light, red banner, for example,
Do not cOlored glasses and solutions modify the
lengths Of the waves or the colors of the rays
sage of some rays, while they permit others to
pass through them.
To dem6nstrate this the lecturer produced a
splendid spectrum on the screen by means Of
the electric light. On interpreting plate Of red
glass, the red Of the spectrum was not made
brighter, but all the other colOrs were eXtn-
gushed. A green solution inteTposed extin-
gushed all the colors of the spectrum but the
green, and a blue solution all but the blue. A
solution made by extracting boiled tea-leaYes
with alcohol absorbed entirely the violet and also
certain shades of crimson, orange and green. The
coloTs which passed through formed q comblna-
OF potash produced FIVE dark bands in the green
of the spectrum. nearly oblterated that color and
consequently the light 1t allowed to pass through
was reddish purple.
Such being the universal laws Of color, It must
have been matter Of no little surprise to the
which, on being illuminated with one kind Of light
or color, exhibited another.
To illustrate this phenomenon, the lecturer ex-
hibited two pictures Of flower with leaves and
buds. The colOrs of one appeared brilliant by
ordinary light while the other was of yellow
n nj q n nnkNa
Illuminating 10th with bright yellow light, the
highly colOred one faded and became as dull as
its companion; but in substituting violet light
remarkable change took place. The cOlOred pic
ture remained dull but the pale one seemed to
glow with splendid red, blue and green hues.
Here, then, substances receive violet light; they
neither absorb nor reflect 1t, but change 1t to red
blue and green. What does this mean?
hne Lecturer tnen iinteTr5gated large screen;
by the electrical light, as to what property it
possessed in reference to light. With green light
and red light the screen gave no answer; but
with blue light the word
FLUoREscEHCE
flashed out in large luminous green letters.
In the experiment Just performed It was only
violet Light or mixture Of blue and violet that
produced the effect. Thousands Of experiments
go to show that violet light alone develops
hOurescence in all bodies capable of exhibiting
this phenomenon, but any color may cause some
the blue color is only excited, SO to speak, by
violet light, the green BY blue rays, and the
and also by the red rays, but not by the interme-
diate ones. From hundreds of such observations
Professor Stokes deduced the law that the ex-
citing light is always of less wave length than
the fuorescent light which It develops.
To show that the invisible actinic rays Of
the spectrum also excited fuOrescence, the Pro-
fessOr projected spectrum from the electric light
on a screen coated with some huorescent sub
stance, in such way as to cause the
Far beyond the visible violet rays the substance
fluoresced with green light. Here, then;we have
method of rendering that region of actfnie rays
visible and amenable to experiment.
In spectrum analysis the metals are recognized
by bright lines in different localities Of the spec
trum. Silver, for example, gives two bright lines
in the green. Stokes discovered that 1t as we'll
as other metals gave lines in the actinic spec
trum also. The lecturer exhibited these lines on
the electric arch, when they came out beautifully
in the huorescent spectrum of the invisible rays.
1t seems to us that, by means Of this extension of
the spectrum, the utility Of that wonderful in
stIument, the spectroseoPe, has been extraordi-
narily increased.
1t follows from these experiments that light
rich in short waves, such as that produced by the
electric discharge in raretied nitrogen, is the
most effective for showing the beauties OF fluo-
resent substances. The lecturer had accordingly
arranged a number Of Geissler tubes, containing
pure nitrogen highly arehed, through which he
passed the electric discharge Of the enormous
Ruhmkortf coil.
Sulphate OF quinine solution. illuminated by
these tubes, glowed with n milky blue Iight al
though II is perfectly transparent.
A2sculin, substance contained in the decoctiOn
or horse-chestnut bark, produces the same effect.
BY means Of this property the one twenty-mil-
liOnth part of nScuiin can be detected in water.
An extract OF the seeds Of stramOnium glOws
with green light.
NORM, a substance extracted from Brazil wood.
lights up with a brilliant green.
Canary" glass, which contains uranium, huO-
resces with a splendid green color.
Many other substances were exhibited with
beautiful effect by Professor Morton: the most re-
markaDle, however, were two recently discovered
by himself, and which he named thallene and
petrOllucene. To these was due the striking
beauty Of the flower exhibited In the early part
OF the lecture.
In order TO study the properties OF fuorescent
bodies the lecturer had examined by means of q
sPeetroseope the light emitted by great number
Of huoTescent substances, which were Illuminated
by beam OF sunlight deprived OF all but the blue
and violet Zig ht by passing through solution of
an moDiosulphate Of copper. He found that @s-
continuous spectra, while those Of the salts OF
uranium, tballene, petrOllucene, &c, were char
acteriZed by bands Of great regularity but differ
ing with different substances, and resembling
their absorption spectra. Curious connections
have been found between the latter and the lumi-
nous bands Of huOrescenCe in certain cases, as for
instance, with alleDe and petrOllucene, as had,
indeed, been already observed in other substances
by Stokes and Hagenbach.
What, then, is fluorescence2
In answer to this question the lecturer pro-
suspended by a thread so as just to touch tun-
ing fork. Then taking another similar tuning
fork, he went off to some distance and sounded it.
The vibrations from this fork travelled through
tiOn was communicated, though with far inferior
rapidity. to the pth ball, whose swinging to and
fro was plainly visible to the audience. In a
similar manner the vibrations OF light might be
conveyed by the lumtniferous ether to q huoTes-
cent body, whose particles would set in motion,
though with diminished velocity, the ether FILL |
ing up the inteTstices between them, thus giving
rise to a color OF lower order.