spectroscope 
fig. -2): this may lie accomplished by combining two crown- 
glass prisms, with a third Iiiiit- K ];i.s prism ,,f an angle of 
Spectroscopes. 
90 between them (fig. 3). For certain rays-for exam- 
ple the yellow -there is no divergence while a spectrum 
is obtained, since the dispersion of the flint-glass prism 
in one direction is greater than that of the two crown- 
glass prisms in the opposite direction. Other forms of 
direct-vision spectroscope have also been devised In 
the grating spectroscope, or di/raclion spectroscope a dif- 
fraction-grating (a series of very flue parallel lines ruled 
on glass or speculum-metal) takes the place of the prism 
and the parallel rays falling upon it are reflected, and 
form a series of diffraction-spectra (see infraction, mat- 
my2, 2, and interference, 5), which are called normal xu'ctm 
(see spectrum, s), since the dispersion of the rays is propor- 
tional to their wave-length. A prism is sometimes used 
before the telescope to separate parts of the successive 
spectra which would otherwise overlap. If a Rowland 
grating (see di/raction) is employed, the arrangements 
can be much simplified, since the large concave surface 
of the grating forms an image directly, which may be re- 
ceived upon a screen, or for study upon a photographic 
plate, or viewed through an eyepiece with cross- wires 
to fix the position of the lines observed. The grating is 
supported at one end of a rigid bar, in practice about 
21 feet in length, at the other end of which, and at the 
center of curvature of the concave surface, is the eye- 
piece or support for the sensitive plate. The ends of this 
bar rest on carriages moving on two rails at right angles 
to each other ; and, as the end carrying the eyepiece is 
moved, the whole length of the spectrum (several feet) 
may be successively observed, the fixed beam of parallel 
rays from the slit falling upon the grating as its position 
is slowly turned. The whole apparatus is mounted on 
rigid supports in a room from which all light but that 
received through the slit is carefully excluded A high 
degree of dispersion is thus obtained, combined with tlie 
advantage of the normal spectrum, and the further advan- 
tages that the amount of light employed is large, while the 
disturbing effect of the absorption of the material of the 
prisms is avoided. See further under spectrum. Analyz- 
ing spectroscope, Integrating spectroscope, tennsap- 
phed to the spectroscope (Young) to describe Its use, with 
or without a lens throwing an image of the luminous ob- 
ject upon the slit. In the former case, different parts of 
the slit are illuminated by light from different parts of 
the object, and their spectra can be separately compared 
or, in other words, the light is thus analyzed ; while in the 
second case, when the collimator is pointed toward the 
source of light, the combined effect of the whole is ob- 
ta " le . u -- H atf-Prisni spectroscope, a spectroscope in 
which the beam of rays enters the prism at right angles 
to one face, and suffers dispersion only on emerging from 
the face opposite and inclined to it. The half-prism ordi- 
narily employed is half of a compound prism such as is 
used in the direct-vision spectroscope. Rainband-SDec- 
troscope. See rainband. 
spectroscope (spek'tro-skop), v. i. and t. ; pret. 
and pp. si>ectroscoi>ed, ppr. spectroscopina. [< 
spectroscope, n.] To use the spectroscope; 
study by means of observations with the spec- 
' Trans - R - 8 - E - 
ing spot will be green ; if black, it will be changed into 
white. These ImtgM are also termed ocular tpectra 
3. lu physics, the continuous band of light (risi- 
ble spectrum) showing the successive prismatic 
colors, or the isolated lines or bands of color 
observed when the radiation from such a source 
as the sun, or an ignited vapor in a gas-flame 
is viewed after having been passed through a 
linsm (prismatic *i>-/i-ii>ii) or reflected from a 
diffraction-grating (diffraction- or interferenee- 
Speetru**)- The action of the prism (see prim, and re- 
fnuttm)lM to refract the light and at the same timr (., 
separate or disperse the rays of different wave-lengths 
the refraction and dispersion being greater as the wave- 
length diminishes. The grating (see 'jratiivj'i, 2), which 
eonsistsusuaHy of a series of tine parallel lines (say 10,000 or 
JO.jXXi to the inch) ruled on speculum-metal, diffracts and 
t the same tnnedisperses the light-rays, forming a series 
of spectra whose lengths depend upon the fineness of the 
.fl'i, ' t W ' a , " o' white light is passed through aslit, 
and then by a col imator lens is thrown upon a prism, and 
H T , r'P '?'" recei ved upon a screen, a colored band 
will be obtained passing by insensible degrees, from the 
.t the '" refrangible end, 
specular 
!. . t i T *C. ^ ' ' llc " lulc reinmgiuie end, 
the violet, through a series of colors ordinarily described 
as red, orange, yellow green, blue, Indigo, and violet. A 
similar effect is obtained from a grating, with, however 
this difference, that in the prismatic spectrum the red 
covers only a sifTall part relatively of the colored band 
since the action of the prism is to crowd together the 
less refrangible rays ami separate the more refrangible 
u ys 5L Iess wav e-length, and thus distort the spectrum. 
Ihe diffraction-spectrum, on the other hand, shows the 
red occupying about the same space as the blue and 
violet, and is called a normal spectrum. When the light 
from different sources is studied in the spectroscope 
It is found, first, that a solid or a liquid when incan- 
descent gives a continuous spectrum, and this is true 
of gases also at great pressures ; second, bodies in the 
gaseous form give discontinuous spectra, consisting of 
colored bright lines (line-spectrum) or bands (band-spec- 
trum), or of bands which under certain conditions ap- 
pear as channeled spaces or flutings (fluted spectrum), and 
these lines or bands for a given substance have a definite 
position, and are hence characteristicof it ; third if light 
from an incandescent solid or liquid body passes through 
a gas (at a lower temperature than the incandescent body) 
the gas absorbs the same rays as those its own spectrum 
consists of ; therefore, in this case, the result is a spectrum 
(absorption-spectrum) continuous, except as interrupted by 
black lines occupying the same position as the bright 
lines in the spectrum of the gas itself would occupy An 
absorption-spectrum, showing more or less sharply defined 
dark bands, is also obtained when the light has passed 
through an appropriate liquid (as blood), or a solid such 
as a salt of didymium (see further under absorption). For 
example, the spectrum from a candle-flame is continuous 
being due to the incandescent carbon particles suspended 
in the flame. If, however, the yellow flame produced 
when a little sodium is inserted in the non-luminous flame 
of a Bunsen burner is examined, a bright-yellow line is 
observed ; if a red lithium flame, then a red and a yellow 
line are seen ; the red strontium flame gives a more com- 
plex spectrum, consisting of a number of lines chiefly in 
the red and yellow ; and so of other similar substances. 
tor substances like iron, and other metals not volatile ex- 
cept at very high temperatures, the heat of the voltaic arc 
is employed, and by this means their spectra, often con- 
sisting of a hundred or more lines (of iron at least 2 000) 
can be mapped out. still again, if the light from the sun 
is studied in the same way, it is found to be a bright 
spectrum from red to violet, but crossed by a large num- 
ber of dark lines called Fraunhofer lines, because though 
earlier seen by Wollaston (1802), they were first mapped 
by Fraunhofer in 1814; this name is given especially to 
the more prominent of them, which he designated by the 
2 3 4 5 
^ 
Could you have spectroscoped a star? 
0. W. Holmes, Atlantic Monthly, XLIX. 387. 
spectroscopic (spek-tro-skop'ik), a. [< spectro- 
scope + -ic.~\ Of, pertaining to, or performed 
by means of the spectroscope or spectroscopy: 
as, spectroscopic analysis; spectroscopic investi- 
gations. 
spectroscopical (spek-tro-skop'i-kal), a. [< 
spectroscopic + -al] Same as spectroscopic. 
spectroscopically (spek-tro-skop'i-kal-i), adv. 
In a spectroscopic manner; by the use of the 
spectroscope. 
spectroscopist (spek'tro-sko-pist), n. [< spec- 
troscope + -ist.'j One who uses the spectro- 
scope ; one skilled in spectroscopy. 
spectroscopy (spek'tro-sko-pi), n. [As spectro- 
scope + -yS.'} That branch of science, more 
particularly of chemical and physical science, 
which is concerned with the use of the spectro- 
scope and with spectrum analysis. 
spectrum (spek'trum), n.; pi. spectra (-tra). 
< NL. spectrum, a spectrum, < L. spectrum, an 
appearance, an image or apparition : see spec- 
ter.'] If. A specter; a ghostly phantom. 2. 
An image of something seen, continuing after 
the eyes are closed, covered, or turned away. 
If, for example, one looks intently with one eye upon any 
colored object, such as a wafer placed on a sheet of white 
paper, and immediately afterward turns the same eye to 
another part of the paper, one sees a similar spot, but 
of a different color. Thus, if the wafer is red the seem- 
II. 
SA^-\^ 
AaBC D Eb F OH 
Fixed Lines and Colored Spaces of Prismatic Spectrum (I.) and 
Normal Spectrum (II.). 
i, red ; 2, red-oransfe ; 3. orange; 4, orange-yellow: 5, yellow; 6, 
cyan-blue; 9, blue and (9%) blue-violet; 10, violet; A, a, B, C, e'tc.' 
Fraunhofer lines. 
letters A to H, etc. (See the figures.) These lines, as ex- 
plained above, are due to the absorption by gases either in 
the sun's atmosphere or in that of the earth. When the 
light is passed through a train of prisms, or reflected from 
a Rowland grating, and thus a very high degree of dis- 
persion obtained, the rays are more widely separated and 
the spectrum can be more minutely examined. Studied in 
this way, it is found that the dark lines in the solar spec 
trum number many thousands, the greater part of which 
can be identified in the spectra of known terrestrial sub- 
stances. Thus, the presence in the sun's atmosphere of 
thirty-six elements has been established (Rowland, 1891) ; 
these include sodium, potassium, calcium, magnesium 
iron, copper, cobalt, silver, lead, tin, zinc, titanium, alu- 
minium, chromium, silicon, carbon, hydrogen, etc. The 
radiation from the sun consists not only of those rays 
whose wave-length is such as to produce the effect of 
vision upon the eye, but also of others of greater wave- 
length than the red rays and less wave-length than the 
violet ; the spectrum from such a source consequently in- 
cludes, besides the luminous part, an invisible part (in- 
visible spectrum) below the red, called the infra-red re- 
gion, and another beyond the violet, called the ultra- 
molel. The first region is also present in the spectrum 
from any hot. body, and the latter in that from a body iit 
a high temperature for example the incandcseent , ai- 
Ixins of an are electric light. Thus. Lanxley by means of 
his bolometer lias proved the existence of rays having a 
wave length nearly twenty times that of the luminous red 
rays, in the radiation of the surface of the moon an ; 
responding to a temperature not far from that .if nu-lting 
ice. Further, while the visible sp.vtiun, includes rays 
separated by only about one octave (since the wave-length 
. for the extreme red is approximately twice that of the ex- 
treme violet), the full spectrum, from the extreme ultra- 
violet to the longest waves recognized by the bolometer 
embraces more than seven octaves. In other words it ex- 
tends from rays having a wave-length of 0.18 of a micron 
to those whose wave-length is so microns (1 micron = 
,(-, millimeter). The invisible regions of the spectrum 
cannot be directly studied by the eye. but they can be ex- 
plored, first by photography, it being possible to prepare 
suitable plates sensitive to the infra-red as well as others 
sensitive to ultra-violet rays, and such photographs show 
the presence of many additional absorption-lincs. The 
invisible infra-red region (heat-spectrum) can also be ex- 
plored by the thermopile and still better the bolometer 
and the distribution of the heat thus examined, and a 
thermogram of the spectrum constructed in which the 
presence* of "cold " absorption-bands is noted Still 
again, the method of phosphorescence is employed to 
give a phosphorograph of the spectrum, while fluores- 
cence is made use of in studying the ultra-violet region 
In studying the invisible heat-spectrum lenses and 
prisms of rock-salt must be used, because the dark rays 
of long wave-length are largely absorbed by glass fur- 
ther, in investigating the invisible ultra-violet region 
quartz is similarly employed, since it is highly transpa- 
rent to these short wave-length vibrations. In many in- 
vestigations it is of great advantage to use the grating- 
spectroscope, especially one provided with a concave 
Rowland grating, since then the normal spectrum (fig II ) 
is obtained directly without the use of the usual lenses 
and prisms, and hence free from their absorbing effects 
Recent photographs of the solar spectrum obtained by 
Prof Rowland in this way give a clearness of definition 
combined with high dispersion never before approached 
Thus, in their enlarged form as published (18HO) the double 
sodium-lines are widely separated, and sixteen distinct 
fine lines may be counted between them. It was for- 
merly the custom to divide the solar spectrum into three 
parts, formed by the invisible heat-rays, the luminous 
rays, and the so-called chemical or actinic rays This 
threefold division of the spectrum is, however largely 
erroneous, since all the rays of the spectrum are "heat- 
rays f they are received upon an absorbing surface, as 
lampblack ; and, while it is true that the chemical change 
upon which ordinary photography depends is most stimu- 
lated by the violet and ultra-violet rays, this is not true 
universally of all chemical changes produced by direct 
radiation. The rays from the lowest end of the spectrum 
to the highest differ intrinsically in wave-length only and 
the difference of effect observed is due to the character 
of the surface upon which they fall. The spectra of the 
stars, of the comets, nebute, etc., can be studied in the 
same way as the solar spectrum, and the result has been 
to throw much light upon the constitution of these bodies 
the spectrum of the aurora has been similarly examined.' 
In addition to its use in the study of cosmical physics 
spectrum analysis has proved a most delicate and invalu- 
able method to the chemist and physicist in the examina- 
r the different elements and their compounds By 
this method of research a number of new elements have 
been detected (as rubidium, cesium, indium, thallium)- 
and recently the study of the absorption-spectra of the 
earths obtained from samarskite, gadolinite, and other 
related minerals has served to show the existence of a 
group of closely related elements whose existence had not 
efore been suspected. Further, the study of the change 
in the spectra of certain elements under different condi- 
tions of temperature has led Lockyer to some most im- 
portant and suggestive hypotheses as to the relation be- 
tween them and their possible compound nature. 
4. [cap.'] [NL.] In zoiil., a generic name va- 
riously used: (a) A genus of lepidopterous in- 
sects. Scopoli, 1777. (6) A genus of gresso- 
rial orthopterous insects: same as Phasma. 
Stall, 1787. (c) A genus of lemuroid mam- 
mals: same as Tarsius. Lacepede, 1803. 5. The 
specific name of some animals, including Tar- 
sius spectrum and Phyllostoma spectrum Fluted 
spectrum. See def. 3. Gitter-spectrum.a diffraction- 
spectrum. Seedef. 3.- Grating-spectrum. See grot- 
l S ff 2 - Herschelian rays of the spectrum. See 
Herschelian. Secondary spectrum, the residual or sec- 
ondary chromatic aberration observed in the use of an 
ordinary so-called achromatic lens (see achromatic), aris- 
ing from the fact that while by combining the crown- and 
flint-glass two of the colors of the spectrum are brought 
to the same focus, the dispersion of the others is not 
equally compensated. By using new kinds of glass which 
allow of proportional dispersion in different parts of the 
spectrum (see apochromatic), Abbe has made lenses which 
collect three colors to one focus, leaving only a small resid- 
ual aberration unconnected, which is called the tertiary 
specula, n. Plural of speculum. 
speculable (spek'u-la-bl), a. Knowable. 
specular (spek'u-lar)', a. [= F. speculaire = 
Pr. specular = Sp. Pg. especular = It. sjieculare, 
< L. specvlaris, belonging to a mirror, < specu- 
lum, a mirror: see speculum.] 1. Of or per- 
taining to a mirror; capable of reflecting ob- 
jects : as, a specular surface ; a specular mineral ; 
specular metal (an alloy prepared for making 
mirrors). 2. Assisting or facilitating vision ; 
serving for inspection or observation ; afford- 
ing a view : as, a specular orb (the eye or a 
lens) ; specular stone (an old name for mica 
used in windows, in Latin specularix lapis); a 
