| 释义 |
isochron, a. and n.|ˈaɪsəʊkrɒn|
Also isochrone |-krəʊn|, 8 erron. -crone.
[f. Gr. ἰσόχρον-ος (see isochronal a.).]
A. adj. (In form isochrone) = isochronous a. 1
1697Evelyn Numism. viii. 281 The Equated Isocrone Motion. 1762tr. Busching's Syst. Geog. I. Pref. 35 The degrees of the meridian, and the lengths of an isochrone pendulum, will always increase together. 1859L. F. Simpson Handbk. Dining vi. (1865) 57 The jaws did not display that isochrone movement which announces good work.
B. n.
†1. An isochronal line. Obs.
a1774Goldsm. Surv. Exp. Philos. (1776) I. 292 Geometricians might make their calculations on several mathematical problems with greater precision, as in Brachystochrones, Isochrones, and such like.
2. A line (imaginary or on a map) connecting points at which a particular event occurs or occurred at the same time.
1881F. Galton in Proc. R. Geogr. Soc. III. 658 Along the coast of West Africa..the ports are regularly served by steamers that touch at every one of them..and which consequently occupy more than forty days to reach even the mouth of the Congo, whereas steamers occasionally sail direct to one or other of those ports in considerably shorter time than these mail steamers. This particular difficulty is met and explained by the sea isochrones, which in this case do not conform to those of the land. 1909Cent. Dict. Suppl., Isochrone, n., a line connecting points at which the same events occur simultaneously. Thus the isochrone of travel is the line connecting points attainable by a person riding or an army marching from a given center forward during a given interval of time; the phenological isochrone, the line connecting points at which plants of any species attain simultaneously the same stage of development. 1948Antiquity XXII. 114 While all competent authorities will agree that the practice of producing food..must have spread in some such way as this map shows, there will be differences of opinion... We expect for instance that the bulge made by the isochrones to include Anau and no more is largely artificial. 1955W. J. Saucier Princ. Meteorol. Analysis xii. 389/1 If the weather occurs along a line, successive positions (isochrones) will be curves on the map. 1956Nature 24 Mar. 571/1 The plots of radio blackout distribution in the North American and North Atlantic region..agree with the isochrons of the ‘morning’ maximum of magnetic disturbance in the Arctic region. 1970Ibid. 17 Jan. 224 The map depicts..the course of withdrawal of the ice sheet from its greatest extent some 18,000 years ago... The detailed isochrons, separated in places by as little as 100 years, graphically depict the north-south corridor that had opened up to the east of the Rocky Mountains about 7,000 years ago.
3. A line (imaginary or on a map) connecting points at which some chosen time interval has the same value.
1940C. A. Heiland Geophysical Explor. ix. 548 Adjusted times are plotted against the location of depth points; points with equal time differences are connected by isochrons which, barring velocity variations and steep dips, give a true picture of the depth contours of the structure. 1945Electronic Engin. XVII. 713/2 Sets of lines can be drawn, joining all the points having the same time-differences; and it has been agreed to call these lines ‘isochrones’, analogous to the ‘isobars’ of a weather-map. In general, these ‘isochrone’ lines are hyperbolae. 1952F. H. Lahee Field Geol. (ed. 5) xxiii. 779 On the assumption that velocity values [of seismic waves] are essentially constant and that reflecting horizons are continuous over a given area, the differences in arrival time from two such horizons can be plotted at each station and then lines of equal time difference (isochrons) can be drawn to produce an isochron map. 1958Jrnl. Brit. Interplanetary Soc. XVI. 340 We have expresed the duration of the voyage in terms of q, ε and n only. In our diagram we can now draw lines of equal duration, which we call isochrones. In Fig. 9 are shown the isochrones for voyages from the Earth to Venus in days.
4. In the isotopic dating of rock, a straight line whose gradient is taken to represent the time since the isotopic content of a sample was fixed (e.g. by crystallization), and obtained by plotting the ratio of the amount of a radiogenic isotope to that of a non-radiogenic isotope against a corresponding ratio for a second radiogenic isotope and the same non-radiogenic one in two or more samples having the same history but different ratios.
1953F. G. Houtermans in Nuovo Cimento X. 1624 By dividing (3b) by (3a) the equations of ‘isochrones’ are obtained... These are a number of straight lines, intersecting at the point αω, βω corresponding to the isotopic constitution of ‘primeval lead’ at the time ω. 1963K. Rankama Progr. Isotope Geol. lxxxvii. 543 When the 207Pb/204Pb ratio was plotted against the 206Pb/204Pb ratio, the slope of the 207Pb = f(206Pb) isochron yielded the age 4·55 Gy for meteoritic matter, and the isotopic constitution of rock lead fell close to the isochron. 1969Bennison & Wright Geol. Hist. Brit. Isles iii. 41 This data can also be presented as isochrons.., the slope of a whole-rock isochron being proportional to the age of initial crystallization and the slope of the mineral isochron to that of the metamorphism. 1971Nature 25 June 500/1 Bofinger..has carried out extensive radiometric dating on illitic sedimentary rocks..; he produced eight separate total-rock Rb-Sr isochrons from seventy-two samples.
5. A line (imaginary or on a map) connecting points on the sea-floor formed at the same time.
1968New Scientist 30 May 452/2 American workers hope eventually to produce a complete ‘isochron’ (lines of equal age) map of the world's oceans. 1972Nature 8 Dec. 339/2 The discharge curve for Iceland was constructed..by extrapolating seafloor spreading isochrons from the ocean floor immediately southwest of the aseismic ridge. |