PH A 



PH A 



Arfvedson. It is a silicate of lithia and 

 alumina. 



PETIOLE. The leaf- stalk of a plant, 

 or that which connects the blade with 

 tlie stem. A leaf so provided is called 

 petiolate ; if otherwise, sessile. When a 

 petiole is divided into several parts, each 

 part hearing a separate leaf or leaflet, it 

 is said to be compound, the stalks of the 

 leaflets being called petiolules or stalk- 

 lets, 



PETITIO PRINCIPII. A non-logical 

 or material fallacy in reasoning, com- 

 monly called begging the question. It 

 takes place when a premiss, whether 

 true or false, is either plainly equivalent 

 to the conclusion, or depends on it for 

 its own reception, as if any one should 

 infer the actual occurrence of the eclipses 

 recorded in the Chinese annals, from an 

 assumption of the authenticity of those 

 annals. Whately. 



PETRIFACTIONS. Stony matters 

 deposited either in the way of incrusta- 

 tions, or within the cavities of organized 

 substances. In the former case, carbo- 

 nate of lime flows over wood and other 

 organic and destructible matters, of 

 which it preserves the form. 



PETROLE'UM (Trtxpa, a rock, eXaiov, 

 oil). Rock oil, an inflammable liquid 

 bituminous substance, differing from 

 naphtha only in being more inspissated. 

 It receives its name from its oozing, like 

 oil, from the rock. It abounds in the 

 United States, where it is known under 

 the name of Seneca or Genessee oil. 



PETRO'SILEX. A name probably 

 given to two different minerals, viz. com- 

 pact quartz and compact felspar; the 

 latter has also been termed fusible petro- 

 silex. 



PETUNTSE'. A species of felspar, 

 constituting the vitrifying ingredient in 

 Chinese porcelain. 



PETWORTH MARBLE. Sussex 

 Marble. A variously coloured limestone, 

 occurring in the weald clay, and com- 

 posed of the remains of fresh-water 

 shells. 



PEWTER. A compound metal formed 

 of tin and lead, in the proportions of 80 

 parts of the former to 20 of the latter. 



PH^NO'GAMOUS {(paivta, to show, 

 7(i)Lio9, nuptials). A term applied to 

 those plants in which the reproductive 

 organs are visible, as distinguished from 

 the cryptogamous, in which they are con- 

 cealed, or of which the function is not 

 understood. The term is synonymous 

 with phanerogamous. 

 25Q 



PHENOMENA {ipaivofxai, to ap- 

 pear). The appearances upon which a 

 system or hypothesis is founded. Thus 

 the apparent motions of the celestial 

 bodies are phaenomena, which have sug- 

 gested the systems of astronomers. A 

 hypothesis, on the contrary, is an assumed 

 cause, by which we endeavour to explain 

 a particular class of phaenomena. 



PHANERO'GAMOUS (0ai/ep69, evi- 

 dent, 7dyuor, nuptials). Phcenogamous. 

 A term applied by botanists to those 

 plants in which the organs of reproduction 

 are easily distinguished. They comprise 

 the exogens and endogens of the natural 

 arrangement. See Cryptogamous. 



PHA'RMACOLITE. Arsenic bloom. 

 Native arseniate of lime, occurring in 

 white acicular crystals, in veins together 

 with tin-white cobalt at Andreasberg, &c. 



PHA'RMACOSIDE'RITE. Arseniate 

 of iron, occurring crystallized, chiefly in 

 cubes, and hence called by Werner cube- 

 ore. 



PHARYNGFNtE LABYRINTHI- 

 FO'RMiE. A family of Acanthopterygi- 

 ous fishes, in which the membranes of 

 the pharynx are divided into small irre- 

 gular leaves, containing cells, which the 

 fish can at pleasure fill with water ; and, 

 by ejecting a portion of this water, it 

 moistens its gills, and is thus enabled to 

 continue its respiration out of its proper 

 element. 



PHASES {(pacrii, an appearance). A 

 term applied in astronomy to the monthly 

 changes of appearance of the moon. 

 When she appears with a full orb, or 

 with all her surface enlightened, we say 

 the moon is full. When a part only of 

 her enlightened hemisphere is towards 

 the earth, and that part is convex, the 

 moon is said to be gibbous (gibbus, 

 bunched out). When a half only of her 

 enlightened hemisphere is visible to the 

 earth, we speak of a half-moon. When 

 a very small portion of the enlightened 

 hemisphere is towards us, and that con- 

 cave, the moon is said to be horned. 

 Lastly, when none of her enlightened 

 hemisphere is towards us, we say the 

 moon changes, or it is new moon. 



When the moon is full, she is said to 

 be in opposition to the sun ; when new, 

 she is said to be in conjunction : these 

 two positions are called syzygies. In the 

 first and the last quarter, half her illu- 

 minated portion is visible; these posi- 

 tions are called quadratures, and the in- 

 termediate points between them and the 

 syzygies are called octants. 



