PAR 



539 



PAR 



upon which they are computed, and it is 

 by menus of the parallactic angles that 

 the astronomer calculates the distances of 

 the heavenly bodies. 



PAR'ALLEI.. Tlaect^X^Xo; . Similarly 

 continued : from trct'a, opposite, and 

 AXjAa>v,.pne another! 1. The term is ap- 

 plied, in geometry, to lines which are 

 everywhere equidistant from each other, 

 and which though ever so far produced 

 would never meet ; and to such planes as 

 have all the perpendiculars drawn be- 

 twixt them equal to each other. Parallel 

 rulers have been contrived for the pur- 

 pose of drawing parallel lines. These are 



of wood, brass, Ac. A B and CD jointed 

 together by cross blades, ac and bd, so 

 adjusted as to allow the rulers to accede 

 and recede, and yet retain their parallel- 

 ism. Parallel coping is a name among 

 masons for such copings as have the 

 upper surface parallel to the bed of the 

 stone, as those upon gables. Parallel 

 motion is a term used by practical mecha- 

 nics to denote the rectilinear motion of a 

 piston rod, &c., in the direction of its 

 length, and contrivances by which such 

 alternate rectilinear motions are con- 

 verted into rotatory ones, and vice versa 

 in pumps, saw mills, and especially in 

 double-acting steam-engines, when the 

 arrangement of parallel rods connected 

 with the piston-rod and the working 

 beam, to transfer the motion of the for- 

 mer to the latter, is now by way of emi- 

 nence termed the parallel motion. 2. 



In astronomy and geography, the parallels 

 of latitude are the circles of latitude (tee 

 LATITUDE). The parallels of altitude are 

 circles parallel to the horizon (see ALMU- 

 CANTERS). The parallels of declination in 

 astronomy are the same as the parallels 

 of latitude in geography. A parallel 

 sphere is that situation of the sphere 

 wherein the equator coincides with the 

 horizon, and the poles with the zenith 

 and nadir. Parallel sailing is a name for 

 the sailing on a parallel latitude (see 



SAILING). 3. We also speak of parallel 



rays in optics; of parallel lines or trenchet 

 in fortification; of historical parallels and 

 parallel passages of scripture, &c. Parallel 

 cut is a name sometimes used for a coun- 

 ter drain. 



PAR'ALLELISM. The state of being pa- 

 rallel. The parallelism of the earth's axis 

 denotes the invariable position of the 

 earth's axis, by which it always points 

 to the same point in the heavens, ab- 

 it the slight effect of muta- 



I tion, &c. To this parallelism we OWP the 

 I vicissitudes of seasons, and the inenua*- 

 ity of day and night. 



PARALLEL'OGRAM, from parallel and 

 y{otftu. A right-lined quadrilateral 

 figure, whose opposite sides are parallel 

 and equal. It receives particular deno- 

 minations, according to the equality or 

 inequality of its sides and angles, as rec- 

 tangle, rhombtts, rhomboid-, and square 

 (q. v.) ; but in common usage the term is 

 applied to quadrilateral figures of more 

 length than breadth, as A B C D, of which 



A D is a diagonal. Parallelogram of 

 forces is a term used to denote the com- 

 position of forces, or the finding of a 

 single force that will be equivalent to two 

 or more given forces when acting in 

 given directions. Thus if a body at A 

 be at the same instant acted upon by 

 two forces represented by A I! and AC, 

 the compound force will be represented 

 by the diagonal line A D. 



PAR'ALLELOPIP'ED, ) from parallel and 



PAR'ALLELOPIP'EDOX, / itri, on, and 

 s-sStfv, a plane. In geometry, a regular 

 solid comprehended under six parallelo- 

 grams (or faces), the opposite ones of 

 which are similar, parallel, and equal to 

 each other; or it is a prism whose base is 

 a parallelogram. 



PARAL'YSIS. ITaaXw<r/s. Palsy: from 

 trotaaXviu, to loosen. A disease known by 

 loss or diminution of the power of volun- 

 tary motion, affecting any part of the. 

 body. Called also Catalysis. 



PARAMA'LE;C ACID, called also fularic 

 and lichenic acid. An acid obtained by 

 keeping malic acid at a temperature of 

 302, when a decomposition ensues, and 

 water and paramaleic acid are the result. 

 The paramaleic acid forms large striated 

 prisms, sometimes rhomboidal,and some- 

 times six-sided. It requires 200 water 

 for its solution, whereas the malic acid 

 dissolves in 100 water. Name ;ra*a, be 

 yond, and malic acid (q. y.) 



PARAM'ETER, from :raa, through, and 

 u,tretat, to measure. A constant right 

 line in each of the three conic sections, 

 called also Latus rectum. 



PARA'VO. A mountainous exposed dis- 

 trict, covered with stunted trees, so 

 termed in South America. In the torrid 



