PER 



PER 



five threads. There are thirteen species, 

 of which P. graeca, common Virginian 

 silk, or periploca, has shrubby twining 

 stems, covered with a dark-coloured 

 bark, sending out slender brandies, 

 twining round each other ; leaves ovate, 

 lanceolate, nearly four inches long, and 

 two broad in the middle ; of a lucid 

 green on their upper side, paler under- 

 neath, opposite, on short foot-stalks ; 

 the flowers appear near the ends of 

 the small branches in bunches of a pur- 

 ple colour, in the months of July and Au- 

 gust. 



PERIPTERAL, in architecture, sur- 

 rounded on all sides with columns, equi- 

 distant from the walls of a building. 



PERISCH, in geography, the inhabi- 

 tants of either frigid zone, between the 

 polar circles and the poles; where the 

 sun, when in the summer signs, moves 

 only round about them, without setting, 

 and consequently their shadows, in the 

 same day, turn to all the points of the 

 horizon. 



PERISTALTIC, in medicine, a ver- 

 micular spontaneous motion of the intes- 

 tines, performed by the conn-action of 

 the circular and longitudinal fibres, of 

 which the fleshy coats of the intestines are 

 composed ; by means whereof the chyle 

 is driven into the orifices of the lacteal 

 veins, and the faeces are protruded to- 

 wards the anus. 



PERITROCHIUM, in mechanics, de- 

 notes a wheel, or circle, concentric with 

 the base of a cylinder, and moveable to- 

 gether with it about an axis. See ME- 

 CHANICS. 



PERIWINKLE. See BUCCINUM. 



PERMIT, a licence or warrant for per- 

 sons to pass with or sell goods, having 

 paid the duties of customs and excise. 



PERMUTATION *f quantities, in alge- 

 bra, the same with combination. See 

 COMBINATION. 



PERORATION, in rhetoric, the epi- 

 logue, or last part of an oration, wherein 

 what the orator had insisted on through 

 his whole discourse, is urged afresh with 

 greater vehemence and passion. The 

 peroration consits of two parts : 1. Reca- 

 pitulation, wherein the substance of what 

 was diffused throughout the whole speech 

 is collected briefly and cursorily, and 

 summed up with new force and weight. 

 2. The moving the passions, which is so 

 peculiar to the peroration, that the mas- 

 ters of the art call this part sedes affec- 

 tuum. The passions to be raised are 

 various, according to the various kinds of 

 oration. In a panegyric, love, admiration,, 



emulation, joy, 8cc. In an invective, ha- 

 trcd, contempt, &c. In a deliberation, 

 hope, confidence, or fear. The qualities 

 required in the peroration are, that it be 

 very vehement and passionate, and that it 

 be short ; because, as Cicero observes, 

 tears soon dry up. 



PEROTIS, in botany, a genus of the 

 Triandria Digynia class and order. Es- 

 sential character : calyx none ; corolla 

 two-valved ; valves equal, avvned. There 

 are two species, viz. P. latifolia, and P 

 polystachya, both natives of the East 

 Indies. 



PERPENDICULAR, in geometry, a 

 line falling directly on another line, so us 

 to make equal angles on each side ; called 

 also a normal line. See GEOMETRY. 



PERPENDICULAR to a parabola, is a 

 right line cutting the parabola in tin: 

 point in which any other right line touches 

 it, and is also itself perpendicular to that 

 tangent. 



PERPETUAL scretv, is one which is 

 acted upon by the teeth of a wheel, and 

 which continues its action for an indefinite 

 length of time, or as long as the teeth of 

 the wheel continue to act upon it. 



PERPETUITY, in the doctrine of an- 

 nuities, is the number of years in which 

 the simple interest of any principal sum 

 will amount to the same as the principal 

 itself; or, it is the number of years' pur- 

 chase to be given for an annuity which is 

 to continue for ever ; and it is found by 

 dividing WQl. by the rate of interest agreed 

 upon: thus, allowing 5 per cent, the per- 



100 

 petuity is , = 20 ; and at the rates 



usually adopted, the perpetuity is as fol^ 

 lows : 



100 

 At 3 per cent. -- = 33.333, &c. 



= 25. 



= 22.22, &c. 



4.5 



f-so. 



6 ^ = 16.66, &c. 



7 152 = 14. 38)& c. 



3?-** 



These are the number of years' pur- 

 chase to be given for a perpetual annui- 



