The times. [volume] (Washington [D.C.]) 1897-1901, 1901-02-17

| as the sodium or Cd lines Combinine
the three essential elements OF the mod
ern spectroscope, the slit. the prism, and
the observing telescope. he saw IN the
spectrum of sunlight IAN almost countless
number OF dark lines" lie was the frst
to use n grating for the production Of
the spectrum, using at frat fine wire graf
ings and afterward ruling fine lines upon
glass. and with these he made the first
accurate measures OF the length OF light
| waves. He did not. however, comprehend
the full import of the problem which he
cists. About twenty years later Sir John
| Herschen studied the bright line spectra
of different substances and found that
they might be used to detect the presence
of minute quantities OF substance whose
| spectrum was known. Wheatstone studied
! the spectrum OF the electric are passing
| between metals, and in 1874 DIR. j. w.
| Draper published very important paper
| on the speetra of solids with increasing
! temperature. Although quite in the dark
| as to the real nature OF the phenomena
| with which they were dealing, these OBJ
servers paved the way for the splendid
/ work of the two Germans kirchon and
Bunsen. who, about 1850, found the key to
| this wonderful problem and made the
science of spectrum analysis substantially
| what II Is today. Its fundamental prin-
| cples may be considered as few and COM
paratively simple
Waves OF light and radiant heat origi-
| nate in ether disturbances produced by
molecular vibration and have impressed
| upon them all of the important qualities
of that vibration. Molecules of different
substances differ in their modes Of vibra-
ton, each producing a wave peculiar TO
and characteristic of Itself. A useful
analogy may be found in the fact that
when one listens to the music OF an or
chestra without seeing it 1t is easy to
Recognize the tones that come from each
of the several instruments. the charac-
teristic vibrations of each being impressed
upon the waves in air which carry the
sound 10 the ear. So delicate and so sure
is this impression of vibration peculiari-
ties that it is even possible to know the
maker of a violin. for instance, by a char
acteristic timbre which must have Its
physical expression in the sound wave.
The ear, more perfect than the eye. an
alyzes the resultant disturbance into its
component parts so that each element may
be attributed to Its proper source I'M
aided the eye cannot do this with Eight.
but the spectroscope separates the various
modes of vibration which make up the
confused whole so that varieties of mole
cular activity are recognizable. The
speed at which source of sound Is ap-
preaching or receding from the ear can be
.f II. f.n
pitch due to the crowding together or
stretching out of the sound waves. and In
the same way the motion of a luminous
body is known from the increase de-
crease of the refrangibility of the elements
of Its spectrum.
Indeed, had nineteenth century science
accomplished nothing else than the dis
covery of spectrum analysis 1t would
have marked the beginning of new
epoch. By this device man is put in COM
munication with every considerable body
in the universe. including even the tn
visible. The "goings on" of Sirius and Al |
gol, of Orion, and the Pleiades are re- |
ported to him across enormous stretches |
of millions of millions OF miles OF space. !
empty save of the ethereal medium itself, |
by this most wonderful wireless telegra- |
ply" And II is by the vibratory motion |
of the invisibly small that all of this is |
revealed; the infinitely little has enabled |
us to conquer the inconceivably big.
Many important contributions to the the |
DRY and practice of spectrum analysis |
have been made since the time OF Kirchoff |
and Bunsen, only two or three of which |
can be referred to here. instrumental |
methods by which spectra are produced
and examined have been greatly perfected,
and this is especially true of what is
known as the "diffraction grating first
used by Frauenhofer. A quarter of CEN
fury ago Rutherford, of New York, con-
structed ruling engine, by means of
which gratings on glass and spectrum
metal were ruled with precision greatly
exceeding what had before been possible. !
A few years later Rowland, of Baltimore
made notable advance In the construc-
ton of a screw far more perfect than any |
before made, producing gratings of a fine
ness and regularity of spacing far ahead
of any others and especially by the capital
discovery of the concave grating by means
Of which the most beautiful results have
been obtained. Very recently Nicholson,
Of Chicago. has invented the Echelon
spectroscope. which, although greatly re-
power of analysis of spectral lines. In his
hands this instrument has been most eff
Iective in the study of the influence of |
strong magnetic field upon the character
# the spectrum from light produced there
n, a most interesting phenomenon first |
observed by Zeeman and one which prom
ses to reveal much concerning the rela- |
ion of molecular activity to light and to
magnetic force.
The development OF spectrum analysis I
vas necessarily accompanied by a recog- c
ition of the identity of radiant heat and
light. The study of radiant heat, which I
vas carried on during the earlier years of | I
he century by Leslie. and later by Melloni
nd Tyndall by what might be called ]
hermal methods, has been industriously | I
pursued during the last two decades by | /
PROCESSES similar to those adopted for G
Usual radiation. The most notable con- v
ribution to this work is the invention of n
he bolometer, by Langley, who at Alle- b
heny and later at Washington. has made | u
Exhaustive studies of solar radiation in O
INVISIBLE regions of the spectrum, espe- +
tally among the waves of greater length | r
han those of red light, where he has c
ound absorption lines and bands similar n
I character to those observed in the WIS., p
Die spectrum. He has also studied the | II
bsorptSon of the earths atmosphere. the | f
citation of energy to visual effect and c.
,any other interesting problems the So Il
ltion of which was made possible by the o
Il