spectrum
(ˈspɛktrəm)
Pl. spectra (also spectrums).
[L. spectrum: see spectre n.]
1. An apparition or phantom; a spectre.
| 1611 Speed Hist. Gt. Brit. ix. xiv. (1632) 770 Walsingham hath written of a fatall Spectrum or Apparition,..where sundry monsters of diuers colours..were seen. 1649 Bulwer Pathomyot. ii. ii. 140 Feare also, and a Sudden fright or Spectrum,..hath the same effect sometimes upon the Muscles of the Face. 1684 Case of Cross in Baptism 14 Startled at Thunder, taken in a storm, frighted with a spectrum. 1706 E. Baynard Cold Baths ii. 309 He would sooner believe Witch-Craft and Spectrums. 1728 Brice's Weekly Jrnl. 19 July 1 The Maid's seeing his Spectrum, could be no..Deceptio Visus, but..was a real Apparition of the Deceased. 1809 W. Irving Hist. New York (1861) 182 Subject to bad dreams..in the night, when the grizzly spectrum of old Keldermeester would stand sentinel by his bedside. 1860 Ruskin Mod. Paint. V. ix. xi. 326 note, Fuseli may wander wildly among gray spectra, but Reynolds and Gainsborough must stay in broad daylight, with pure humanity. |
| fig. 1657 H. Pinnell Philos. Ref. 67 The Spectrum, ghost, or fantasie, the Light of Nature. 1674 Grew Anat. Pl., Disc. Mixture (1684) 222 Their notions of Mixture..being..so many phantastick Spectrums, serving only to affright men from coming near them. 1710 Sacheverell Answ. Bp. Oxford's Sp. 21, I was..surpriz'd..with an Apparition or Spectrum, which the Magi call a Parenthesis. 1866 Huxley Physiol. x. 247 Many persons are liable to what may be called auditory spectra—music of various degrees of complexity sounding in their ears, without any external cause, while they are wide awake. |
2. An image or semblance.
rare.
| 1693 Penn Fruits Solitude ii. §197 A jealous man only sees his own spectrum, when he looks upon other men, and gives his character in theirs. 1831 Carlyle Sart. Res. ii. viii, Two little visual Spectra of men, hovering..in the midst of the Unfathomable. |
3. a. The coloured band into which a beam of light is decomposed by means of a prism or diffraction grating. Also, a dark band containing bright lines produced similarly; such a (coloured or dark) band, or the pattern of lines in it, as characteristic of the light source; hence, the pattern of absorption or emission of light or other electromagnetic radiation over any range of wavelengths exhibited by a body or substance.
| 1671 Newton in Phil. Trans. VI. 3076 Comparing the length of this coloured Spectrum with its breadth, I found it about five times greater. 1674 Ibid. IX. 218 The Sunbeams..passing through a Glass Prism to the opposite Wall, exhibited there a Spectrum of divers colours. 1728 Pemberton Newton's Philos. 323 These colours shall discover themselves more perfectly..the larger the spectrum is. 1788 V. Knox Winter Even. I. iii. 27 All the hues of the prismatic spectrum. 1815 J. Smith Panorama Sci. & Art I. 440 It assumes an oblong shape,..and exhibits seven different colours. This oblong image is called the spectrum, and from its being produced by the prism, the prismatic spectrum. 1824 Edin. Philos. Jrnl. X. 39 Lines are also seen in the spectrum of other fixed stars of the first magnitude. 1839 G. Bird Nat. Philos. 326 The solar spectrum may therefore be regarded as composed of three spectra of equal lengths over-lapping each other. 1879 Cassell's Techn. Educ. I. 126/1 Most of our sources of artificial light yield spectra without lines. 1879 Encycl. Brit. X. 215/1 When the light of a burning metal is examined with a properly-arranged prism, it is seen to give a dark band or spectrum which is traversed by certain vertical bright lines. 1900 Proc. R. Soc. LXVI. 45 The expected argon spectrum was almost entirely absent. 1925 G. A. Lindsay tr. Siegbahn's Spectroscopy of X-Rays vi. 195 X-ray spectra afford one of the most direct sources of information concerning the inner structure of the atom. 1966 McGraw-Hill Encycl. Sci. & Technol. VIII. 420/2 Microwave spectra of atoms can be used to measure..nuclear electric and magnetic moments. 1971 Physics Bull. July 401/1 The laser spectrum extends from the vacuum ultraviolet to the far infrared. 1978 Pasachoff & Kutner University Astron. xxviii. 709 All the lines in the spectrum of 3C 48 were shifted by 37 per cent, a still more astounding redshift. |
| fig. 1860 Holland Miss Gilbert's Career iv. 68 All the colors of the spectrum of truth. 1874 H. R. Reynolds John Bapt. viii. 453 A luminous spectrum lingers for a while in the atmosphere of Judaism. |
b. The entire range of wavelengths (or frequencies) of electromagnetic radiation, from the longest radio waves to the shortest gamma rays of which the range of visible light is only a small part; any one part of this larger range.
| 1888 Encycl. Brit. XXIII. 142/1 When a telescope is to be constructed for photographic purposes the aim should be to unite..the rays near that portion of the spectrum which act most powerfully on the photographic plate. 1923 Glazebrook Dict. Appl. Physics IV. 891/1 Beyond the photographic limit, investigation of the infra-red spectrum by means of the heating effect of the rays has been carried on. 1947 Sci. News IV. 54 The wave lengths of the visible spectrum, from red over yellow, green, blue to violet, lie between 700 and 350 millionths of a millimetre. 1962 Rep. Comm. Broadcasting 1960 i. 5 in Parl. Papers 1961–2 (Cmnd. 1753) IX. 259 The division by international agreement of the frequency spectrum into bands allocated to particular services forms part of the International Radio Regulations. 1978 Pasachoff & Kutner University Astron. ii. 21 The new ability that astronomers have to study parts of the electromagnetic spectrum other than light waves enables us to increase our knowledge of celestial objects manyfold. |
c. An actual or notional arrangement of the component parts of any phenomenon according to frequency, energy, mass, or the like.
Cf. mass spectrum s.v. mass n.2 10 d,
power spectrum s.v. power n.1 18
f.| 1887 Science 11 Mar. 238/1 It is proposed to analyze a composition by forming what may be called a ‘word⁓spectrum’, or ‘characteristic curve’, which shall be a graphic representation of an arrangement of words according to their length and to the relative frequency of their occurrence. 1897 J. J. Thomson in Phil. Mag. XLIV. 297 When the cathode rays are deflected by the electrostatic field, the phosphorescent band breaks up into several bright bands separated by comparatively dark spaces; the phenomena are exactly analogous to those observed by Birkeland when the cathode rays are deflected by a magnet, and called by him the magnetic spectrum. 1933 Proc. R. Soc. A. CXLII. 347 A large number of experiments was made to determine the distribution of α-particles over the whole of the spectrum, which includes α-particles of ranges between 7 cm. and 12 cm. 1939 Psychol. Rec. III. 60 Fig. 1 shows the acoustic spectra of three tones of the same singer and vowel, sung at the three different intensity levels at approximately the same frequency. 1962 A. C. Gimson Introd. Pronunc. Eng. iii. 21 The spectrum above 4,000 cps would appear to be largely irrelevant to the recognition of our vowels. 1971 Nature 3 Sept. 2/2 The idea..is that even quite small explosions can be distinguished from earthquakes of comparable size by the high frequency parts of their seismic spectra. 1973 Williams & Fleming Spectrosc. Methods in Inorg. Chem. (ed. 2) iv. 181 In many cases, convenient starting points for counting the spectrum are the peaks at m/e 28 (N2+) and m/e 32 (O2+). |
d. fig. The entire range or extent of something, arranged by degree, quality, etc.
| 1936 R. Campbell Mithraic Emblems 20 Their sistered stridences ignite The spectrum of the poets' lyre. 1952, etc. [see broad-spectrum a. s.v. broad D. 2]. 1958 Listener 28 Aug. 308/2 At the other end of the political spectrum Lloyd Warner has used similar methods in his nostalgic account of the status system of old New England. 1964 G. L. Cohen What's Wrong with Hospitals? i. 18 Theoretically, students remain long enough on each type of ward to give them a spectrum of experience. 1971 Sci. Amer. July 25/2 At the polar ends of the age spectrum—children and ‘senior citizens’—the trends at the moment are following different courses. 1979 Practical Woodworking Mar. 42 P― hand tools embrace a wide spectrum of products. |
4. The image retained for a time on the retina of the eye when turned away after gazing fixedly for some time at a bright coloured object.
| 1786 Phil. Trans. LXXVI. 313 This appearance in the eye we shall call the ocular spectrum of that object. 1829 Nat. Philos., Optics xvii. 46 (L.U.K.), One of the most curious affections of the eye, is that in virtue of which it sees what are called ocular spectra, or accidental colours. 1839 G. Bird Nat. Philos. 398 Thus wafers, or other coloured objects, produce spectra of colours complementary to their own. 1854 Lardner's Mus. Sci. & Art I. 85 Unreal objects will often be perceived. These are called spectra. Ibid., This object is an optical spectrum. |
5. Ent. A spectre-insect (
Phasma).
| 1838 Murray's N. Germany 34 The minerals and insects are also good; among the latter are various specimens of spectrum, nearly a foot long. |
6. Math. (See
quots.)
| 1948 P. R. Halmos Finite Dimensional Vector Spaces ii. 79 The set on n proper values of A, with multiplicities properly counted, is the spectrum of A. 1972 A. G. Howson Handbk. Terms Algebra & Anal. xvii. 83 The set of all eigenvalues of a linear transformation t of a finite-dimensional vector space V is known as the spectrum of t. |
7. attrib. (in sense 3):
a. spectrum analysis (
cf. spectral a. 6). Also
fig.| 1866 Atkinson tr. Ganot's Physics 425 The method of spectrum-analysis is most readily applied to the alkaline metals. 1871 tr. Schellen's Spectrum Anal. Pref. 4 The great merit of the book as a popular treatise on Spectrum Analysis. 1873 Farrar Famil. Speech ii. 39 The microscope and spectrum analysis of Philology. |
b. Misc., as
spectrum allocation,
spectrum-band,
spectrum-line,
spectrum microscope,
spectrum photography,
spectrum work.
| 1871 tr. Schellen's Spectrum Anal. 101 The number of the spectrum-lines of a substance. Ibid. 456 Qualitative Analysis..by means of the spectrum microscope. 1889 Anthony's Photogr. Bull. II. 389 The bath plate is less suitable for spectrum photography. 1891 Ibid. IV. 357 The yet hardly visible spectrum band. 1899 Lockyer in Daily News 13 Nov. 6/7 For this spectrum work very rapid isochromatic plates..should be employed. 1960 McGraw-Hill Encycl. Sci. & Technol. XI. 260/1 (caption) Radio spectrum allocations. 1980 Sci. Amer. Feb. 32/1 The control of interference lies at the heart of spectrum allocation, which entails the development of systematic plans for the use of frequencies in radio communication. |
8. Special
Comb.:
spectrum analyser, a device which analyses a system of oscillations into its spectral components.
| 1942 Radiation Lab. (Mass. Inst. Technol.) Man. No. m–115 (title) Spectrum analyzer (Type 103) for pulsed oscillators at 3,000 Mc/sec. 1973 Times 14 Dec. 8/8 So far they had spent 150 man-hours in preliminary work, setting up ‘spectrum analysers, computers, graphical displays and other advanced equipment’. |