PNE 
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 plu- 
rality or number of things. See Gram- 
mar. 
PLURALITY. In ecclesiastical mat- 
ters, no person having one benefice, with 
cure of souls, of 81. a year, in the King’s 
books, shall accept another ; but the for- 
mer benefice shall be void, unless the per- 
son has a dispensation from the Archbishop 
of Canterbury, who has power to grant dis- 
pensations to chaplains of noblemen and 
others, under proper qualifications, 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, +, used for the sign of addition. 
PLUSH, in commerce, &c. a kind of 
stuft' 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 goal’s or camel’s hair; though 
there are some plushes entirely of worsted, 
and others composed wholly of hair. Plush 
is manufactured, like velvet, on a loom with 
three treadles ; two of these separate and 
depress the woollen warp, and the third 
raises the hair warp, upon which the work- 
man throwing the shuttle, passes the woof 
between the woollen and hair warp ; and 
afterwards laying a brass broach, or needle, 
under that of the hair, he cuts it thereon 
rvith a knife destined for that use ; conduct- 
ing 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 tliat branch of natu- 
ral 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 celebrated philosopher hav- 
ing injected air into a glass vessel, so that it 
there remained compressed, found that the 
vessel weighed more than when the contained 
PNE 
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 
indebted for the invention of this elegant 
machine, which is not, like many others, 
confined to one part of experimental philo- 
sophy, for almost all branches derive aid 
from it. This machine, which will be pre- 
sently described, when reduced to its great- 
est simplicity, is composed of a vertical 
cylinder of brass, in which a piston is mo- 
ved ; 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 ex- 
haust the air, which is executed by making 
the piston descend and ascend alternately. 
By the use of this instrument, the gravity 
of the air has been verified, by first weigh- 
ing a ball or bladder full of air, and then 
weighing it, after the ball or bladder has 
been exhausted of the air: a sensible dimi- 
nution will be perceived in the weight of 
the ball. Philosophers have attempted like- 
wise to determine, with precision, the spe- 
cific gravity 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 experiments 
of Lavoisier, it follows that a cubic inch of 
air, taken at 10 degrees of Reaumur, weighs 
0.46005 grains, and that the weight of a 
cubic foot of the same fiuid is one ounce, 
three drams, and three grains; but by some 
very accurate experiments of Mr. Caven- 
dish, it was ascertained that the weight of 
water is to that of air as 800 to 1 : this was 
the case when the barometer stood at 29| 
inches, and the thermometer at !y0°. Sir 
George Shuckburgh found it to be as 836 
to 1, when the barometer was 29.37, and 
the thermometer at 51°. The medium of 
many experiments by the gentlemen al- 
ready mentioned, and by Mr. Hauksbee, 
Dr. Halley, Mr. Cotes, and other philoso- 
phers equally zealous in the improvements 
of natural science, is about 832 to 1, when 
the barometer is 30°, and the thermometer 
55° : this ratio must vary in proportion to 
the changes in the height of the barometer, 
and it varies also ^th part for every de- 
