| 释义 |
Lambert|ˈlæmbət|
[The name of Johann Heinrich Lambert (1728–77), German mathematician.]
1. a. In Cartography used attrib. and in the possessive to designate certain map projections devised by Lambert, spec. a conical conformal projection having two standard parallels along which the scale is true. Also ellipt. as Lambert.
1879Encycl. Brit. X. 207/2 A translation of this essay [of Gauss's] is to be found in the Philosophical Magazine for 1828.., where Lambert's projection comes out as a particular solution of the general problem. 1912A. R. Hinks Map Projections ii. 18 When the conical orthomorphic projection is used, it is always that with two standard parallels, which is Lambert's second, or Gauss'. 1953A. H. Robinson Elem. Cartogr. iii. 43 The Lambert conic projection..has concentric parallels and equally spaced straight meridians that meet the parallels at right angles... It has two standard parallels, but the spacing of the other parallels on the Lambert increases away from the standard parallels. Ibid. iv. 74 The Lambert azimuthal equal-area projection is most useful when centered in the area of interest. 1971I. G. Gass et al. Understanding Earth xv. 224 (caption) A possible geometrical fit of the southern continents at the 500-fathom..contour... Lambert equal area projection.
b. In Physics used in the possessive to designate two laws enunciated by Lambert: (a) the intensity of the light emitted by an element of area of a perfectly diffusing surface is proportional to the cosine of the angle between the direction of emission and the normal to the surface; (b) (see quots. 1911, 1966).
1895Electrician 20 Sept. 672/2 The diffused reflection practically follows Lambert's cosine law. 1911R. W. Wood Physical Optics (rev. ed.) xv. 437 Lambert's law states that each layer of equal thickness absorbs an equal fraction of the light which traverses it. 1952R. W. Ditchburn Light xv. 441 Experimental observations on the transmission in a homogeneous medium which absorbs, but does not scatter, the light are summarized in Lambert's law, which may be written L(z) = L0e-2αz. The constant 2α is called the absorption coefficient. 1966D. G. Brandon Mod. Techniques Metallogr. ii. 65 The fraction of the incident intensity transmitted through a thin slice, of thickness t, can be calculated from Lambert's law: I/I0 = exp(-µt), where µ is the absorption coefficient.
2. (Written lambert.) A unit of luminance equal to one lumen per square centimetre (equivalent to approximately 3180 candelas per square metre).
1915P. G. Nutting in Electr. World 6 Feb. 333/1, I prefer to speak of a brightness of so many ‘lamberts’. This term is now well understood in our laboratory. Where required it is easily translated into lumens and any desired units of area. 1915H. E. Ives in Ibid. 20 Feb. 460/1 Dr. Nutting..comes forward with an excellent name,..the ‘lambert’. But he applies it, in my opinion, to the wrong unit... Let us say that a surface has a brightness of one ‘lambert’ if it is as bright as a ‘Lambert's law’ white surface under unit illumination. 1923L. C. Martin Colour 178 The normal radiation corresponds to 1/π candles per square centimetre when the brightness is 1 lambert. 1953Amos & Birkinshaw Television Engin. I. 280, 1 lambert = 1 lumen per square centimetre = 0·3183 candle per square centimetre = 2·054 candles per square inch = 929 foot-lamberts. 1962F. I. Ordway et al. Basic Astronautics iii. 37 (table) Sun... Surface brightness, lamberts... 6·24 × 105. 1966D. G. Brandon Mod. Techniques Metallogr. i. 58 Haine gives the minimum practical screen brightness [of an electron microscope] as 3 × 10-4 lamberts. |