Page:Cyclopaedia, Chambers - Supplement, Volume 2.djvu/900

 PEA

the habk of one part from that of another. But fome moderns have denied the exigence of a Parenchyma, or pulpy matter, nnd have aflerted, that the whole body is competed of veflels and canals. The chief promoter of this opinion was Ruyfch, who having laid the injected parts of the body in rectified fpirit of wine, and then dried them in the air; whatever was not injected, was thereby diffipated, and the remainder con- futed merely of veflels; from whence he concluded, that the whole was compofed of veflels. But it feems certain, that a .pofed of canals. If indeed, after injection, it be fuftercd to dry, the parts not injected will exhale, and the more the mufcle is dried, the more it will appear compofed of veflels. What is here faid of a mufcle, holds true of all other parts of the body. Thus many veflels run through the fubftance of a bone"; but'no one' has yet been able to demonftrate, that the whole bone is compofed of veflels. There always re- mains a fiibftance peculiar to bones, which has never yet been fhewn to be vafcular. In the brain alfo there always remains
 * frefh mufcle can never be fo injected, as to appear wholly com-

' fomething which cannot he demonftrated vafcular.

The Parenchyma is fenfibly full of juices, fo that very little of truly folid matter remains, when thefe juices are ex* haled.

TAKlS-herb, in botany, the name of a diftinct genus of plants.

" See the article Herba Paris, Suppl.

PAROTID- glands. In a fuppuration of thefe, one caution only is needful; namely, to open the abfeefs, as foon as it can be fuppofed to have formed matter; without waiting for a fluctuation, or even foftnefs of the tumour, that may never happen; the pores being here fo very vifcid, that after it is ripe, the part will feel as hard as if the fuppuration had not

■ begun. Pringle, Obferv. on the Difeafes of the Army, p. 277.

PARROQUET, in ornithology, the name by which we call the fmaller fpecies of Parrots. Sec the article Psitt acus, Suppl.

There are a great number of diftinct fpecies of Parroquets, as well as of Parrots, which having got peculiar names, are de- fcribed under their refpective articles.

PARSLEY (Suppl.)— Ba/iard-? arsley, the name of a genus of plants, known among botanifts by that of Caucalis, bee the article Caucalis, Suppl.

Corn-? arsley, Field-? arsley, and Maeedonuin-1? ARSLEY, names ufed by fome for a fpecies of Slum. See the article Sium, Suppl.

Pool's-? arsley, the name given hy fome writers to a fpecies of Cicuta, or hemlock. SeethearticIeCicuTA, Suppl.

Macedonian-? arsley, the name by which *he Myrrbis 6f bo- tanifts is fometimes called. See the article Myrrhis, Suppl. 1

Mountain-? arsley, the Englifh name of a genus of plants, called by botanifts OreofsUnum. See the article Oreose-


 * LINUM, Suppl.

PARSL1NG, on fhip-board, fmall pieces of old canvas, cut four inches broad, and wrapped about fhrouds, flays, ftraps for blocks, &c. before ferved with fpun yarn. Blanck- /^'sNav. Expof. p. 115.

PARSNEP( Suppl) — Cows-? ar's n e p, the Englifli name of a diftindt genus of plants, called by botanifts Sphondylium. See the article Sphondylium, Suppl.

Sea or Prickly-lmulod Parsnep, names given to the Echino-. phora of botanifts. See the article Echinophosa, Suppl.

/^c/«--Parsnep, the name ufed by fome for a fpecies of Sium, See the article Sium, Suppl.

P ASSIGN -jlower, the Englifli name of a genus of plants, cal- led by botanifts Granadilla. See the article Gr akadjlla, Suppl.

PASTE (Suppl.) — Chryfolite Paste. See the article Chry- solite, Append.

PASTINACHA (Suppl) — is alfo ufed for the carrot, or Daucas of botanifts. See the article Daucus, Suppl

PEA (Suppl ) — EverlaJling-PEA, or Earth-nut Pe a, names fometimes given to the Lathyrus. See the article La- th YRUS, Suppl.

Heart-? E a, or Bladder-? 'e a-, names by which the Corhdum of botanifts is fometimes called. See the article Corindum, Suppl

Indian-? e a, the name by which a fpecies of Orobus is fometimes called. See the article Orobus, Suppl.

Pigeon-? e a, a name fometimes given to the Cytifus, or fhrub- trefoil. See the article Cytisus, Suppl.

Sesrlet-?EA, in botany, the Englifh name of a genus of plants, called by Linnaeus Glycine. See the article Glycine, Suppl.

J¥inged*?EA, a name by which fome call the Lotus. See the article Lotus, Suppl.

PEACOCK, in ornithology, the Englifh name of a genus of birds, called by zoologilts Paw. See the article Pavo, Suppl.

pEACOCK-fifi, the Englifli name of a fifti of the Turdus, or wrafle-kind. See the article Pavo, Suppl.

?EAR( Suppl)— Prickly-V 'ear, a name fometimes ufed for the

PEN

Opuniia Cereus, Mehcattus, he. all comprehended by Linnae- us under that of Catlus. See the article Cactus, Suppl, and Append.

PEUALES. See the article Abbot, Cycl.

PEEVIT, the Englifli name of a bird of the Larus, or gull- kind, with a black head, and grey coloured body. Sec the article Larus, Suppl

PELLITORY of Spain, the Englifli name of a genus of plants called by different authors Cbamamelum and Buphthalmum. Linnaeus defcribes it under this laft. See the article BUPH- THALMUM, Suppl.

The root of this plant is known in the fhops by the name of Pyrethrum. See the article Pyrethrum, Suppl.

Double PellitoRY, a name fometimes given to the Ptarmica, or fnetzewort, of botanical writers. See the article Ptar- mica, Suppl

PENDULUM (Cycl and Suppl.) — Huygens having difcovcr- ed that the vibrations of a Pendulum movingin a cycloid, would be performed in equal times, even tho' the vibrations were unequal, this principle was applied to the conftruction of Pendulum-c\ock$; but great inequalities were ftill obferved in their motions; and' many years pafied before any fuccefsful attempts were made to remedy thele irregularities. The late excellent artirt Mr. George Graham apprehending, that the irregularities in the motions of clocks airofe from a change of length in the Pendulum, by the influences of heat and cold made feveral trials in order to dtfeover whether there was any confiderable difference of cxpanfion between brafs, fteel, iron ■ filver, &c. when expofed to the fame degrees of heat; con- ceiving that it would not be very difficult, hy making ufe of two forts of metals differing conhdcrably in their degrees of expanfioh and contraction, to remedy, in a great meafure, the irregularities to which common, Pendulums are fubject. But no hopes of fuccefs arifing from the experiments he then made, he turned his thoughts to the application of the obfer- vatiuns he had made about the .extraordinary expansion of quicklilver by heat, and be found out a proper method of applying a column or that iluid to the Pendulum of a clock in order to prevent the irregularities arifing from its different lengths by the effects of heat and cold, which fucceeded ex- tremely well, and is what is now called Mr, Graham's £huck- Jiher Pendulum.

After this, Mr. John Harrifon, of Barrow, in Lincclnfhire one of the molt ingenious artiffs of the age, and famous for his invention of the clock for finding the difference of longi- tude at fea, without having the leaft knowledge of what ]\?r. Graham had done before him, made feveral experiments upon wires of different metals, in order to find their different de- grees of expanuon and contraction. He thought that by a proper combination of wires of two different metals, differ- ing confiderably in their cxpanfion and contraction, hemisht be enabled to keep the center of ofcillation of a Pendulum\\~ ways at the fame diffance, from the point of fufpenflon. ' In cortfequence of thefe experiments, he made a Pendulum con- fiding of one fteel wire, at the end of which is the bob or weight; and on each fide of this wire, four wires alternately biafs and fteel, fo difpofed and contrived, as to raife the Pen- dulum by the fame quantity that it is lengthened by heat, and to let down the Pendulum in the fame proportion as it is raifed by cold.

Mr. Harrifon, in his ffift machine for meafuring time at fea likewife applied this combination of wires of brafs and fteel to prevent any alterations by heat and cold. And in the two machines or clocks he has iince made for the fame purpofe a like niLthcd of guarding againft the irregularities arifing from this caufe is ufed.

Mr. Graham alfo made a Pendulum confiffing of three bars one of fteel between two of brafs, and the itcel bar acted upon a lever, fo as to raife the Pendulum, when lengthened by heat, and to let it down, when fliortened by cold; but he found this clock liable to Hidden ftarts and jerks in its motion, bee Mr. Short, in the Phil. Tranf. vol. 47. p. 517. feq. who there alfo mentions a Pendulum of this kind made by Mr. Fo- theringham, a quaker in Lincolnfliire. The ingenious Mr. Ellicot a has given a defcription of twa methods ufed by himfelf, by which the irregularity of the mo- tion of a clock, arifing from the influence of heat and cold, upon the rod cf the Pendulum, may be prevented. Mr. Elli- cot tells us, that having by many experiments with his pyro- meter " found a great difference between the expanffon of brafs and iron, he made a Pendulum compofed of thofe two metals and applied it fo fucceisfully to regulate the motion of a clock, that he avoided all the jerks to which it was fufpected the mo- tion of the machine would be liable. [ a Phil. Tranf. vol. 47. p. 479. feq. b See the article Pyrometer, Append.] Befldes the irregularities arifing from heat and cold, Pendulum- clocks are liable to others from friction, and from foulnefs, owing to the oil ufed. But Mr. Harrifon has feveral excel- Jent contrivances by which his clocks are almoit entirely free from friction; and therefore he ufes no oil, fo that there is no neceflity of ever cleaning. See Mr. Short, ubi fu-pra. See alfo Monf. Caffini, in'Mem. Acad. Scienc. 1741.

PEN-