CUR 



CUR 



by the action of which it receives a brown 

 stain. 



CU'RCUMINE. The colouring matter 

 of turmeric, obtained in a state of purity 

 by separating it from its combination 

 with oxide of lead. 



CURD. The coagulum which sepa- 

 rates from milk, upon the addition of 

 acid, rennet, or wine. 



CURRENTS, ATMOSPHERIC. Dis- 

 turbances of the atmospheric mass from 

 regular or accidental causes. 1. Regular 

 or periodical currents are the trade-winds, 

 monsoons, sea and land breezes, which 

 are caused by the rotatory motion of the 

 globe being greater than that of the air, 

 by the combined attraction of the sun 

 and moon producing tides in the atmo- 

 sphere, &c. 2. Irregular currents are 

 ordinary winds, produred by variations 

 of temperature or of electrical distribu- 

 tion, and have frequently a circular or 

 rotatory motion. 



CURRENTS OF THE SEA. Certain 

 motions of the sea, which are independent 

 of the tides, and named drift- currents 

 and stream-currents. 



1. Drift-currents are motions produced 

 on the surface of the sea by the perpetual 

 or the prevailing winds. Thus, in the 

 Atlantic Ocean, a drift-current occurs 

 between the tropics, where it is produced 

 by the trade-wind; other drift-currents 

 occur to the north and the south of 30°, 

 where they are ascribed to the effects of 

 the prevalent winds. 



2. Stream-currents are motions pro- 

 duced to a great depth, perhaps to the 

 bottom, of the sea ; their causes are con- 

 sequently unknown. Amongst these 

 may be noticed the equatorial current, 

 running from the coast of Africa to that 

 of South America; and the gulf-stream, 

 flowing from North America to the shores 

 of Europe. 



CURRENTS, SUBTERRANEAN. 

 Subterranean currents of water, sup- 

 posed to be the cause of the formation of 

 caverns in limestone districts by gra- 

 dually wearing away the rock in the 

 course of fissures. 



CURSO'RES {cMr5M5, a course). Cours- 

 ers ; an order of birds, so named from 

 their remarkable velocity in running. 

 They were included by Cuvier in the 

 Grallatoreg, or Waders, probably on ac- 

 count of the length of their legs. They 

 comprise tlie ostrich, the cassowary, the 

 emu, the apterix, and the dodo. These 

 birds exhibit the nearest approach to 

 the Mammalia. [Under 



97 



Under the term Cursores, Walcknaer 

 arranges those spiders which make no 

 webs, but catch their prey by swift 

 pursuit. 



CURSO'RIA {cursus, a course). A 

 family of Orthopterous insects, the legs 

 of which are all alike, and adapted for 

 running. They include the ear-wig, the 

 cockroach, and the mantis. See Salta- 

 toria. 



CU'RTATE {curtatus, shortened). A 

 term sometimes applied, in Geometry or 

 Astronomy, to a line projected ortho- 

 graphically upon a plane. 



Curtate Distance, in Astronomy, de- 

 notes a planet's distance from the sun, 

 reduced to the plane of the ecliptic. 



CURVE {curvus, bent). A term ap- 

 plied to a line of which no portion, how- 

 ever small, is straight. A crooked line 

 may be either a curved line, or the junc- 

 tion of two or more straight lines drawn 

 in different directions. The principal 

 curves are the circle, the ellipse, the 

 parabola, the hyperbola, and the cycloid. 



1 . Curve, Algebraic and Transcendental. 

 1. Algebraic curves are those in which 

 the relation between the abscissa and the 

 ordinate is expressed by an algebraic 

 equation. 2. Transcendental curves are 

 those in which the relation between x 

 and y is not expressed by an algebraic, 

 but by a differential equation ; that is, by 

 an equation between dx and dy. 



2. Curve, Evolute and Involute of. If 

 a thread, having one of its ends fixed, be 

 wound round a curve, this primary curve 

 is called the evolute. If the thread, thus 

 tightly applied upon the convexity of the 

 curve, be then unwound, it will describe 

 a secondary curve at the back of the 

 former, termed the involute. It will be 

 seen that the thread, at every point of 

 unwinding, is a tangent to the evolute. 



3. Curve, Equation of. An algebraic 

 expression, pointing out the relation be- 

 tween the ordinate and the abscissa. In 

 every conic section, these two lines are at 

 right angles to each other ; and at what- 

 ever point of the axis (in the same sort 

 of curve) the ordinate may be drawn, 

 these two lines will always have the same 

 relation to each other. 



4. Curves of Double Curvature. Curves 

 traced on surfaces which are not plane : a 

 double curvature thus arises, viz. that 

 belonging to the line itself, and that of 

 the surface on which it is traced. 



5. Curve Surfaces. A curve surface 

 is represented algebraically by an equa- 

 tion containing three variables, as x, y, 



F 



