QUA 



magnesia, found among volcanic rocks. 

 It has received various names. 



14. Pyro-phorous. A terai applied to 

 certain substances which, by the absorp- 

 tion and condensation of the aqueous 

 vapour and gases contained in the atmo- 

 sphere, become heated and ignited, as 

 spongy platinum, which absorbs hydro- 

 gen and oxygen so readily, and then 

 condenses them, that its entire mass 

 becomes red-hot, and the gas is ignited. 



15. Pyro-phyllite. A green radiated 

 variety of talc from Siberia, composed of 

 distinct groups of small diverging la- 

 minaB. 



16. Pyro-physalite. A sub-species of 

 prismatic topaz, from Fahlun in Sweden. 



17. Pyro-somata {awfxa, a body). A 

 family of the Tunicata, consisting of 

 minute animals aggregated together in 

 great numbers, so as to form a hollow 

 cylinder, which swims in the sea by the 

 combined contractions and dilatations of 

 all the individuals composing it, and is 



QUxi 



capable of emitting in the dark a brilliant 

 phosphorescent light, or body of fire, as 

 the name denotes. 



18. Pyro-techny (rexvn, art). The art 

 which teaches the management and ap- 

 plication of fire to certain operations ; a 

 term commonly applied to the prepara- 

 tion of artificial fireworks. 



PYRULI'N^. Pear-shells; a sub- 

 family of the Turbinellidse, or Turnip- 

 shells, named from the typical genus 

 pyrula, and characterized by the short- 

 ness of the spire, by the smoothness and 

 convexity of the pillar, and by the mode- 

 rate length of the canal. 



PYXI'DIUM {pyxis, a box). A fruit 

 which dehisces by a transverse incision, 

 so that, when ripe, the seeds and their 

 placenta appear as if seated in a cup, 

 covered by an operculum or lid, as in 

 hyoscyamus, anagallis, &c. 



PY'XIS NAUTICA. The Mariner's 

 Compass; a modern southern constella- 

 tion, placed in Argo. 



a 



QUADRANT {quadrans, a quarter). 

 A quadrant, in Geometry, is a quarter of 

 a circle. The term also denotes an in- 

 strument for measuring angles, consist- 

 ing of a quarter circle of wood or metal, 

 having its circular part, or limb, divided 

 into 90 parts, or degrees, and these sub- 

 divided into minutes, &c., by means of 

 a Nonius or a Vernier. 



1. Hadley's Quadrant is properly an 

 octant^ or eighth part of a circle, in 

 which the angles are taken by means of 

 the reflexion of light ; and when the 

 limb is extended to 60 degrees (the sixth 

 of a circle), the instrument is called a 

 Sextant. 



2. Quadrant of Altitude. The name 

 given to a flexible graduated slip of brass, 

 which is fixed to the brazen meridian of 

 the globe. By this the distance from one 

 point of the globe to another can be ob- 

 tained in degrees of arc. But as other 

 arcs besides altitudes may be measured 

 with it, it is sufficiently distinguished by 

 calling it the flexible arc. 



QUADRANT ELECTROMETER. 

 An instrument for estimating the degree 

 or intensity of electricity, invented by 

 Mr. Henley. The differences of electric 

 intensity are denoted by an index which 

 278 



traverses a quadrant divided into ninety 

 equal parts, called degrees. 



QUADRA'NTAL. A name formerly 

 given to spherical triangles, one side of 

 which is a quadrant. 



QUADRA'TIC EQUATIONS. Qua- 

 dratic equations are divided into pure 

 and adfected. Pure quadratic equations 

 are those which contain only the square 

 of the unknown quantity, as a;2 = 36 ; 

 a;2 -I- 5 = 54 ; ax'^—b = c; &c. Adfected 

 quadratic equations are those which in- 

 volve both the square and the simple 

 power of the unknown quantity, as x^+ 

 4ar = 45; 3a:2 — 2x = 2l; ax'^ + 2bx = 

 c + d; &c. 



QUADRA'TRIX. A name given to 

 a curve which may be employed in the 

 quadrature of other curves. Some of 

 these have been specified ; but, after all, 

 the description of these curves assumes 

 the point which they are intended to de- 

 termine. 



QUADRATURE (in Astronomy). The 

 moon is said to be in her quadrature, 

 when she is in either of the middle points 

 of her orbit, between her conjunction 

 and opposition, since lines from the earth 

 to the moon and to the sun include a 

 quadrant, or 90 degrees. Her face is 



