spectrum

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. Physics The distribution of a characteristic of a physical system or phenomenon, especially:
2. n. Physics The distribution of energy emitted by a radiant source, as by an incandescent body, arranged in order of wavelengths.
3. n. Physics The distribution of atomic or subatomic particles in a system, as in a magnetically resolved molecular beam, arranged in order of masses.
4. n. A graphic or photographic representation of such a distribution.
5. n. A range of values of a quantity or set of related quantities.
6. n. A broad sequence or range of related qualities, ideas, or activities: the whole spectrum of 20th-century thought.

Century Dictionary and Cyclopedia

1. n. A specter; a ghostly phantom.
2. n. 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 seeming spot will be green; if black, it will be changed into white. These images are also termed ocular spectra.
3. n. In physics, the continuous band of light (visible 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 prism (prismatic spectrum) or reflected from a diffraction-grating (diffraction- or interference-spectrum). The action of the prism (see prism and refraction) is to refract the light and at the same time to separate or disperse the rays of different wave-lengths, the refraction and dispersion being greater as the wavelength diminishes. The grating (see grating, 2), which consists usually of a series of fine parallel lines (say 10,000 or 20,000 to the inch) ruled on speculum-metal, diffracts and at the same time disperses the light-rays, forming a series of spectra whose lengths depend upon the fineness of the lines. If, now, a beam of white light is passed through a slit, and then by a collimator lens is thrown upon a prism, and the light from this received upon a screen, a colored band will be obtained passing by insensible degrees, from the less refrangible end, the red, to the more refrangible 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 small part relatively of the colored band, since the action of the prism is to crowd together the less refrangible rays and separate the more refrangible rays of less wave-length, and thus distort the spectrum. The 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 incandescent gives a continuous spectrum, and this is true of gases also at great pressures; second, bodies in the gaseous form give discontinnous spectra, consisting of colored bright lines (line-spectrum) or bands (band-spectrum), or of bands which under certain conditions appear as channeled spaces or flutings (fluted spectrum), and these lines or bands for a given substance have a definite position, and are hence characteristic of 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 complex spectrum, consisting of a number of lines, chiefly in the red and yellow; and so of other similar substances. For substances like iron, and other metals not volatile except at very high temperatures, the heat of the voltaic are is employed, and by this means their spectra, often consisting 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 number 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 letters A to H, etc. (See the figures.) These lines, as explained 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 dispersion 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 spectrum number many thousands, the greater part of which can be identified in the spectra of known terrestrial substances. 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, alumininm, 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 wavelength than the red rays and less wave-length than the violet; the spectrnm from such a source consequently includes, besides the lnminons part, an invisible part (invisible spectrum) below the red, called the infra-red region, and another beyond the violet, called the ultra-violet. The first region is also present in the spectrum from any hot body, and the latter in that from a body at a high temperature—for example the incandescent carbons of an arc electric light. Thus, Langley by means of his bolometer has 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, and corresponding to a temperature not far from that of melting ice. Further, while the visible spectrum includes rays separated by only about one octave (since the wave-length for the extreme red is approximately twice that of the extreme violet), the full spectrum, from the extreme ultraviolet to the longest waves recognized by the bolometer, embraces more than seven octaves. In other words, it extends from rays having a wave-length of 0.18 of a micron to those whose wave-length is 30 microns (1 micron = millimeter). The invisible regions of the spectrum cannot be directly studied by the eye, but they can be explored, 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-lines. The invisible infra-red region (heat-spectrum) can also be explored 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 fluorescence 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, further, in investigating the invisible ultra-violet region quartz is similarly employed, since it is highly transparent to these short wave-length vibrations. In many investigations 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 nse 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 (1890), the double sodium-lines are widely separated, and sixteen distinct fine lines may be counted between them. It was formerly 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” if 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 stimulated 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, nebulæ, etc., can be stndied 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 invaluable method to the chemist and physicist in the examination of the different elements and their compounds. By this method of research a number of new elements have been detected (as rubidium, cæsium, 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 before been suspected. Further, the study of the change in the spectra of certain elements under different conditions of temperature has led Lockyer to some most important and suggestive hypotheses as to the relation between them and their possible compound nature.
4. n. In zoology, a generic name variously used:
5. n. A genus of lepidopterous insects.
6. n. A genus of gressorial orthopterous insects: same as
7. n. A genus of lemuroid mammals: same as
8. n. The specific name of some animals, including Tarsius spectrum and Phyllostoma spectrum.
9. n. That portion, of any spectrum, which consists of rays less refrangible than the longest wave-lengths of the visible spectrum.

Wiktionary

1. n. A range; a continuous, infinite, one-dimensional set, possibly bounded by extremes.
2. n. chemistry The pattern of absorption or emission of radiation produced by a substance when subjected to energy (radiation, heat, electricity, etc.).
3. n. mathematics, linear algebra The set of eigenvalues of a matrix.
4. n. mathematics, functional analysis Of a bounded linear operator A, the set of scalar values λ such that the operator A—λI, where I denotes the identity operator, does not have a bounded inverse; intended as a generalisation of the linear algebra sense.

GNU Webster's 1913

1. n. obsolete An apparition; a specter.
2. n. The several colored and other rays of which light is composed, separated by the refraction of a prism or other means, and observed or studied either as spread out on a screen, by direct vision, by photography, or otherwise. See Illust. of Light, and Spectroscope.
3. n. A luminous appearance, or an image seen after the eye has been exposed to an intense light or a strongly illuminated object. When the object is colored, the image appears of the complementary color, as a green image seen after viewing a red wafer lying on white paper. Called also ocular spectrum.

WordNet 3.0

1. n. an ordered array of the components of an emission or wave
2. n. a broad range of related objects or values or qualities or ideas or activities