FLU 
1 tvhich they serve to close ; and to these is 
joined a little copper tube about two inches 
long, and of the thickness the leaden pipe is 
intended to be of. By means of these tubes 
the core is retained in the middle of the ca- 
vity of the mould. The core being in the 
mould, with the rundles at its two ends, and 
the lead melted in the furnace, they take it 
up in a ladle and pour it into the mould by a 
little aperture at one end, made in the form 
of a funnel. When the mould is full, they 
pass a iiook into the end of the core, and 
; turning the mill, draw it out ; and then open- 
ing the mould, take out the pipe. If they 
desire to have the pipe lengthened, they put 
one end of it in the lower end of the mould, 
and pass the end of the core into it ^hen 
shut the mould again, and apply its ^Rlle 
and tube as before, the pipe just cast serving 
foi rundle, &c. at fhe other end. Things 
being thuJMilaced, they pour in fresh metal, 
and repeatire operation til! they have got a 
pipe of the length required. 
For making pipes of sheet-lead, the plumb- 
ers have wooden cyUhders of the ||ngth and 
thickness required, and on these they form 
their pipes by wrapping the sheet around 
them, and soldering up the edges all along 
them. See Pipe. 
PLUMERIA, a genus of the pentandria 
monogyma class of plants, the corolla of 
which consists of a single funnel-like petal, 
with a long tube, and divided into live ob- 
long segments at the limb : the fruit is com- 
posed of two jointed and ventricose follicles, 
form d of a single valve each, and containing 
numerous oblong seeds. There are four 
species. 
PLUMMET, plumli-rule or plumb-line, 
an in trument used by carpenters, masons, 
&c. in order to judge whether walls. &c. are 
upright planes, horizontal, or the like. It 
is thus called from a piece of lead, plum- 
bum, fastened to the end of a cord, which 
usually constitutes this instrument. Some- 
times the string descends along a wooden 
ruler, &c. raised perpendicularly on another, 
in which case it becomes a level. See 
Level. # 
PLUMMING, among miners, is the me- 
thod of using a mine-dial, in order to know 
the exact place of the work where to sink 
down an air shaft, or to bring an adit to the 
work, or to know which way the load in- 
clines when any hexure happens in it. 
It is performed in this manner: A skilful 
person, with an assistant, and with pen, ink, 
and paper, and a long line, and a sun-dial, 
after his guess of the place above ground, 
descends into the adit or work, and there 
fastens one end of the line to some fixed 
thing in it ; then the incited needle is let to 
rest, and the exact point where it rests is 
marked with a pen ; he then goes on farther 
in the line still fastened, and at the next tiex- 
ure on the adit he makes a mark on the line 
bv a knot or otherwise ; and then letting 
down the dial again, he there likewise notes 
down that point at which the needle stands in 
this second position. In this manner he 
proceeds, from turning to turning, marking 
down the points, and marking the line, till 
lie comes to the intended place ; this done, 
he ascends and begins to work on the surface 
Of the earth what he did in the adit, bring- 
ing the first knot in the line to such a place 
flI 
where the mark of the place of the needle 
will again answer its pointing, and continues 
this till he comes to the desired place above 
ground, which is certain to be perpendicu- 
larly over the part of the mine into which 
the air-shaft is to be sunk. 
PLUNGER, in mechanics, the same with 
the forcer of a pump. See Pump. 
PLURALITY. If any person having one 
benefice with cure of souls of eight pounds a 
year in the king’s books, shall accept another 
of whatsoever value, and be instituted and 
inducted into the same, the former benetice 
shall be void ; unless he has a dispensation 
from the archbishop of Canterbury, who has 
power to grant dispensations to chaplains of 
nob ! emen 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 resides in each 
for a reasonable time every year, and that he 
keeps a sufficient curate in that in which he 
does not ordinarily reside. 
PLUS, in algebra^ character marked 
thus -f-, used for the sign of addition. See 
Character. 
PLUSH, in commerce, &c. a kind of 
stuff leaving 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 goats 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 se- 
parate and depress the woollen warp, and 
the third raises the hair warp, upon which 
the workman throwing the shuttle, passes 
the woof between tiie woollen and hair warp; 
and afterwards laying a brass broach, or 
needle, under that or the hair, he cuts it 
with a knife destined for that use ; conducting 
the knife on the broach, which is made a 
little hollo^ all its length, and thus gives 
the surface of the plush an appearance of 
velvet. See Velvet. 
There are other kinds of plush, all of silk ; 
some of which have a pretty long knap on 
one side, and some on both. 
PLUVIAMETER, a machine for mea- 
suring the quantity of rain that falls. Fig. 16, 
Plate I. Pneumatics, shews the section ol a very 
good pluviameter. It consists of a hollow 
cylinder, having within it a cork ball attach 
cd to a wooden stem, which passes through 
a small opening at top, on which is placed 
a large tunnel. v When this instrument is 
placed in the open air in a free place, the 
rain that falls within the circumference of 
the funnel will run down into the tube, and 
cause the cork to iloat, and the quantity oi 
water in the tube may be seen by the height 
to which the stem of fhe float is raised. 
The stem of the ttoat is so graduated, as to 
shew by its divisions the number of perpen- 
dicular inches of water which fell on the 
surface of the earth since the last obser- 
vation. 
A very simple pluviameter, and which will 
answer all practical purposes, consists 
simply of a copper funnel, the area of whose 
opening is exactly ten inches ; this funnel is 
fixed in a bottle, and the quantity of rain 
caught is ascertained by multiplying the 
weight in ounces by .173, which gives the 
depth in inches and parts of an inch. 
P N E 455 
PNEUMATICS. Though the word 
pneumatics means, strictly, th^^science 
which treats of the properties of gene- 
ral, yet it is commonly used to express the 
mechanical properties of elastic or aeriform 
fluids ; such as their weight, density, com- 
pressibility, and elasticity. The other pro- 
perties ot elastic fluids are treated of under 
Chemistry and Air. 
The air is a fluid in which we live and 
breathe : it entirely envelopes our globe, 
and extends to a considerable height around 
it. 1 ogether with the clouds and vapours 
that float in it, it is called the atmosphere. 
As it is possessed of gravity in common with 
all other fluids, it must press upon bodies 
in proportion to the depth at which they are 
immersed in it ; and it also presses in every 
direction, in common with all other fluids. 
It differs from all other fluids in the four 
following particulars: 1. It can be compress- 
ed into a much less space than it naturally 
possesses ; 2. It cannot be congealed cir 
fixed as other fluids may ; 3. It is of a differ- 
ent density in every part upward from the 
earth’s surface ; decreasing in its weight, bulk 
for bulk, the higher it rises ; 4. It is of an* 
elastic or springy nature, and the force of its 
spring is equal to its weight. 
Few people who are unacquainted with the 
principles of natural philosophy, suppose 
that tiie air by which we are surrounded is 
a material substance, like water, or any other 
visible matter. Being perfectly invisible, 
and affording no resistance to the touch, it 
must seem to them extraordinary, to consider 
it as a solid and material substance ; and yet 
a few simple experiments will convince any 
one that it is really matter, and possesses - 
weight, and the power of resisting other bo- 
dies that press against it. 
Take a bladder that has not the neck tied, 
and you may press the sides together, 
and squeeze it into any shape. Fill this 
bladder with air, by blowing into it, and 
tie a string fast round the neck : you then 
find that you cannot, without breaking the 
bladder, press the sides together, and that 
you can scarcely alter its” figure by any 
pressure. Whence then arise these effects? 
When the bladder was empty, you could 
press it into any form; but the air with 
which it is filled, prevents this : the resist- 
ance you experience when it is filled with 
air, proves that that is real matter as well as 
any other substance that we are acquainted 
with. 
We are accustomed to say, that a vessel is 
empty, when we have ponied out of it the 
water which it contained. Throw a bit of 
cork upon a bason ot water, and having put 
an empty tumbler over it with the mouth 
downwards, force it down through the wa- 
ter ; the cork will shew the surface of the 
water within the tumbler, and you will see 
that it wih not rise so high within as without 
the glass ; nor, if y ou press ever so hard, 
will it rise to the same level. The water 
is, therefore, prevented from rising within 
the tumbler, by some other substance which 
already occupies the inside ; which substance 
is the air that filled the tumbler when it was 
inverted, and which could not escape, on ac- 
count of the superior pressure of the water. 
In like manner, having opened a pair o? 
common bellows, stop up tiie nozzle se- 
