PAR 



PAR 



scent to the centre of the earth would 

 elevate her 58' above the rational horizon 

 drawn through the centre. 



3. Parallax, angle of. In Optics, the 

 angle of parallax is that angle which the 

 axes of the eyes, when directed towards 

 an object, form with it at their point of 

 contact. This angle becomes greater as 

 the object is nearer. 



PARALLELETIPED (irapaWy^Xeiri- 

 irebov, a body with parallel surfaces). A 

 hexahedron, all whose faces are paral- 

 lelograms, and each pair of faces which 

 do not actually intersect are parallel. A 

 prism whose bases are parallelograms is 

 called a parallelepiped. If the bases of 

 a rectangular parallelepiped be squares, 

 and the attitude be equal to the side 

 of the base, all its faces will be squares, 

 and such a parallelepiped is called a cube. 



PARALLE'LOGRAM (7rapaXAf»\6- 

 7paMMof> bounded by parallel lines). A 

 quadrilateral figure, whose opposite sides 

 are parallel. The term, as thus defined, 

 is applicable to the square, the rectangle 

 or oblong, the rhombus or lozenge, and 

 the rhomboid ; but these terms are sig- 

 nificant of relations existing between the 

 angles, as well as the sides of the figures. 



PARALLELS (TrapaXArjXof, beside 

 one another, side by side). In Astro- 

 nomy, the term Parallels denotes those 

 circles which every point of the earth 

 between its poles describes by its diurnal 

 rotation, and which run, as it were, side 

 by side of one another. 



Parallels Mathematical. Parallel right 

 lines are such as are in the same plane, 

 and which, being produced continually 

 in both directions, would never meet. 



PARA'METER (Trapajuexpeo), to mea- 

 sure by, or with, another thing). A term- 

 originally applied to a constant straight 

 line belonging to each of the conic sec- 

 tions, and synonymous with latus rec- 

 tum; that is, the perpendicular drawn to 

 the axis through a focus, terminated both 

 ways by the curve, was the parameter of 

 the curve. The term was afterwards 

 applied, in a general sense, to the con- 

 stant quantity which enters into the 

 equation of a curve. In the language of 

 astronomy, what were formerly called 

 the parameters of the orbits, are now 

 generally called their elements. 



PARASI'TA. The Louse tribe; an 

 order of " familiar " insects, which are 

 entirely wingless, do not undergo meta- 

 morphosis, but agree with the true in- 

 sects in having only six legs. The term 

 parasite, derived from wapd, and aiTOf, 

 249 



provisions, denotes, in its original sense, 

 a hanger-on at the tables of the great. 



PARATO'NNERE. The French term 

 for a lightning conductor, or metallic rod, 

 made to project above the highest part 

 of a building, and continued down to the 

 ground ; its object being to promote the 

 discharge of an electric cloud, and to 

 conduct the lightning to the ground 

 without injuring the building. 



PARE'NCHYMA (TrapeYXf/^a* any 

 thing poured in beside). The name given 

 by Erasistratus to the peculiar substance 

 of the lungs, liver, kidneys, and spleen, 

 as \i formed separately by the blood of 

 veins which run into those parts : the 

 word <rapf he used only of the muscular 

 flesh. The term is generally applied to 

 the soft tissue of organs, in plants and 

 animals, particularly to that of the 

 glands. 



PARHE'LION (Trapa, near, nXtor, the 

 sun). A mock sun, or meteor, of a 

 brilliant light, resembling the sun, and 

 occasionally accompanying hales. The 

 term parhelion denotes an image of the 

 sun formed by reflection from a cloud. 



PARIE'TAL {paries, a wall). A term 

 applied to any thing which is attached to 

 the wall of an organ, as to the placenta 

 of plants, when attached to the walls of 

 the ovary, as in poppy, violet, &c. 



PA'RINiE {parus, the tit). Parine 

 birds or Tits ; a family of the Cantairicea 

 of >Iacgillivray, somewhat allied to the 

 kinglets and the jays, although, from 

 their diminutive size, they seem at first 

 sight to have little affinity to the latter. 



PARI-PINNATE. Equally pinnate, 

 abruptly pinnate; applied to a pinnate 

 leaf of which the petiole is terminated 

 neither by a leaflet nor a tendril. 



PARO'NYMOUS WORDS (Trapwi/v- 

 /i09, formed from a word by a slight 

 change). Words which belong to one 

 another, as the substantive, adjective, 

 verb, &c. of the same root. These have 

 not in every case a precisely corre- 

 spondent meaning, and the careless or 

 designed application of them may lead to 

 the logical fallaciafigurcE dictionis, which 

 properly belongs to the case of Ambi- 

 guous Middle. Thus, " Projectors are 

 unfit to be trusted : this man has formed 

 a project ; therefore he is unfit to be 

 trusted." Here the sophist proceeds on 

 the hypothesis that he who forms a pro- 

 ject must be a projector: whereas the 

 bad sense which commonly attaches to 

 the latter word, is not at all implied in 

 the former. Whately. 



M5 



