PISE 



PNE 



PLUNGER, in mechanics, a solid brass 

 cylinder, u$e<l as a forcer in forcing 1 

 pumps. 



PLURAL, in grammar, an epithet ap- 

 plied to that number of nouns and verbs 

 which is used when we speak of more 

 than one thing- ; or that which expresses 

 a plurality or number of things. See 



PLURALITY. In ecclesiastical mat- 

 ters, no person having- one benefice, with 

 cure of souls, of 8/. a year, in the King's 

 books, shall accept another ; but the for- 

 mer benefice shall be void, unless the 

 person has a dispensation from the Arch- 

 bishop of Canterbury, who lias power to 

 grant dispensations to chaplains of noble- 

 men and others, under proper qualifica- 

 tions, to hold two livings, provided they 

 are not more than thirty miles distant 

 from each other; and provided that he 

 reside in each, for a reasonable time, 

 every year; and that the parson keep a 

 sufficient curate in that in which he does 

 not ordinarily reside. 



PLUS, in algebra, a character marked 

 thus -J-, used for the sign of addition. 



PLUSH, in commerce, &c. a kind of 

 stuff having a sort of velvet knap, or 

 shag, on one side, composed regularly of 

 a woof of a single woollen thread and a 

 double warp, the one wool, of two threads 

 twisted, the other goat's or camel's hair; 

 though there are some plushes entirely 

 of worsted, and others composed wholly 

 of hair. Plush is manufactured, like vel- 

 vet, on a loom with three treadles ; two 

 of these separate and depress the wool- 

 len warp, and the third raises the hair 

 warp, upon which the workman throw- 

 ing the shuttle passes the woof between 

 the woollen and hair warp ; and after- 

 wards laying- a brass broach, or needle, 

 under that of the hair, he cuts it thereon 

 with a knife destined for that use ; con- 

 ducting the knife on the broach, which 

 is made a little hollow all its length, and 

 thus gives the surface of the plush an 

 appearance of velvet. See VELVET. 

 PLUVIAMETER. See RAIN gauge. 

 PNEUMATICS, is that branch of na- 

 tural philosophy which treats of the 

 weight, pressure, and elasticity of the air, 

 with the effects arising from them. 



Galileo, whose name is presented as of 

 itself, whenever the enquiry relates to 

 the first researches concerning gravity, 

 had verified that of the air, which was 

 denied almost universally before him, 

 though it had been discovered by some 

 few philosophers of antiquity. This cele- 

 brated philosopher having injected air 



into a glass vessel, so that it there re* 

 majned compressed, found that the vessel 

 weighed more than when the contained 

 air was in its natural state. He inquired 

 also, by another experiment, into the 

 heaviness of this fluid compared with that 

 of water ; but he found it only in the 

 ratio of 1 to 400, which is much too small, 

 as we shall soon see. The pneumatic 

 machine, or air-pump, was not then 

 known. It is to Otto Guericke, a burgo- 

 master of Magdeburg, that we are in- 

 debted for the invention of this elegant 

 machine, which is not, like many others, 

 confined to one part of experimental phi- 

 losophy, for almost all branches derive 

 aid from it. This machine, which will 

 be presently described, when reduced to 

 its greatest simplicity, is composed of a 

 vertical cylinder of brass, in which a pis- 

 ton is moved; its upper base carries a 

 cock, above which is soldered a circular 

 brass plate situated horizontally. On this 

 plate the receiver is placed, from which 

 we would exhaust the air, which is exe- 

 cuted by making the piston descend and 

 ascend alternately. By the use of this 

 instrument, the gravity of the air has been 

 verified, by first weighing a ball or blad- 

 der full of air, and then weighing it, after 

 the ball or bladder has been exhausted of 

 the air; a sensible diminution will be 

 perceived in the weight of the ball. Phi- 

 losophers have attempted likewise to de- 

 termine, with precision, the specific gra- 

 vity of the air. 



According to the results of Deluc, the 

 ratio between the weight of common air 

 and distilled water, at the temperature of 

 thawing ice, and under a medium pres- 

 sure of 29.9 English inches of mercury, 

 is that of 1 to 760 ; and from the experi- 

 ments of Lavoisier, it follows that a cubic 

 inch of air, taken at 10 degrees of Reau- 

 mur, weighs 0.46005 grains, and that the 

 weight of a cubic foot of the same fluid is 

 one ounce, three drams, and three grains, 

 but by some very accurate experiments 

 of Mr. Cavendish, it was ascertained that 

 the weight of water is to that cf air as 

 800 to 1 : this was the case when the 

 barometer stood at 29| inches, and the 

 thermometer at 50. Sir George Shu :k- 

 burgh found it to be as 836 to 1, when 

 the "barometer was 29.37, and the thermo- 

 meter at 51. The medium of many ex- 

 periments by the gentlemen already 

 mentioned, and by Mr. Hauksbee, Dr. 

 Halley, Mr. Cotes, and other philosophers 

 eoually zealous in the improvements of 

 natural science, is about 832 to 1, when 

 the barometer is 30, and the thermpme- 



