?' U M 
PUM 
PUM 
nor can the structure of the legs be contem- 
plated without admiration. 
Though it would perhaps be difficult to 
prove that there exists in Europe more than 
one genuine species of tlea, yet it is certain 
that some permanent varieties or races may 
be traced, which a practised eye can readily 
distinguish from the « common domestic kind. 
Of these the most remarkable seems to be 
that infesting some of the smaller quadrupeds, 
and particularly mice and bats. Tins variety 
is of a more slender form than the common 
tiea, and ol' a paler colour, differing from that 
insect nearly in the same proportion that a 
greyhound does from the more common race 
of dogs. 
Puiex penetrans, or chigger, is a native of 
South America and the West Indian islands. 
According to Catesby’s microscopic figure of 
this insect, it may properly be arranged un- 
der the present genus; but it is probable, 
from the different descriptions of authors, 
that some insects of the genus acarus, which 
excite similar swellings under the skin, have 
been confounded with it under the general 
name of chigger or chigoe. Catesby’s ac- 
count runs as follows: 
“ It is a very small flea, that is found Only 
in warm climates. It is a very troublesome 
insect, especially to negroes, and others that 
go barefoot and are slovenly. They pene- 
trate the skin, under which they lay a bunch 
or bag of eggs, which swell to the bigness of 
a small pea or tare, and give great pain till 
taken out ; to perform which great care is 
required, for fear of breaking the bag, which 
endangers a mortification, and the loss of a 
leg, and sometimes life itself. This insect, in 
its natural size, is not above a fourth part so 
big as the common flea. From the mouth 
issues a hollow tube like that of the common 
tlea, between a pair of antennas. It has six 
jointed legs, and something resembling a tail. 
The egg is so small as to be scarcely dis- 
cerned by the naked eye. These chegoes 
are a nuisance to most parts of America be- 
tween the tropics.” 
PULLEY. See Mechanics. 
PULMONARIA, lungwort, a genus of 
the monogynia order, in the pentandria class 
of plants, and in the natural method ranking 
under the 41st order, asperifolias. The co- 
rolla is funnel-shaped, with its throat per- 
vious ; the calyx is prismatic and pentagonal. 
There are seven species, of which the most 
remarkable is the officinalis, common spotted 
lungwort, or Jerusalem cowslip. This is a 
native of woods and shady places in Italy and 
Germany, but has been cultivated in Britain 
for medical use. The leaves are of a green 
colour, spotted with white ; and of a muci- 
laginous taste, without any smell. They are 
recommended in phthisis, ulcers of the lungs, 
&c. but their virtues in these diseases are 
not warranted by experience. 
PULSATILLA. See Anemone. 
PULSE, in the animal economy, denotes 
the beating or throbbing of the heart and ar- 
teries. See Physiology. 
Pulse. Seel.EGUMEN. 
PULTEN.LA, a genus of the class and 
order decandria monogynia. The calyx is 
five-toothed ; corolla papilionaceous ; le- 
gume one cell, two-seeds. There are six 
species, shrubs of New Holland. 
PUMICE-STONE, or porous glasses. 
When tjie compact glasses are exposed to the 
heat of our furnaces, they emit a great ntup- 
ber of air-bubbles, which renders them 
porous: such is the origin of pumice. It 
has the same base as compact glass. The 
texture is fibrous ; the fibres have a silky 
lustre. Colours various ; white, brown, vel- 
Iow, black. Before the blow-pipe, they 
melt into a white enamel. According to 
Klaproth, the pumice consists of 
77.:‘)0 silica 
17.50 alumina 
1.75 oxide of iron 
3.00 potass 
99-75. See Fulmination. 
PUMP, an hydraulic machine for -raising 
water by means of the pressure of the atmo- 
sphere. It would be an entertaining and not 
an uninstructive piece of information to learn 
the progressive steps by which the ingenuity 
of man has invented the various methods of 
raising water. A pump must be considered 
as the last step of this progress. Common 
as it is, and overlooked even by the curious, 
it is a very abstruse and refined invention. 
Nothing like it has been found in any of the 
rude nations whom the Europeans have dis- 
covered, either in the new continent of 
America or the islands of the Pacific Ocean. 
Nay, it was unknown in the cultivated em- 
pire of China at the time of our arrival there 
by sea; and it is still a rarity every where in 
Asia, in places unfrequented by the Euro- 
peans. It does not appear to have been 
known by the Greeks and Romans in early 
times ; and perhaps it came from Alexandria, 
-where physical and mathematical science 
was much cultivated by the Greek school 
under the protection of the Ptolemies. The 
performances of Ctesibius and Hero are 
spoken of by Pliny and Vitruvius as curious 
novelties. There are two sorts of pumps, 
which essentially differ ; and all the varieties 
are but modifications of these. One has a 
piston with a perforation and valve ; the other 
•has a solid piston: to the former is given the 
name of the common sucking-pump ; the 
latter is denominated the forcing-pump. 
Fig. 1. represents the common sucking- 
pump. AA is a cylinder of cast iron, bored 
smooth withinside ; it has a tianch at the top, 
by which it is screwet^to the wooden cistern 
B, which conveys the water away from the 
pump. It has also a flanch D at its lower 
end, to screw on the pipe E, which brings 
the water to the pump. In the same tianch 
is a pair of valves, aa ; and the bucket or 
piston E, which slides within the barrel, has 
another similar pair of valves in it. This 
bucket is screwed to an iron rod G, which is 
moved up and down by some machine. 
When the bucket F descends, its valves bb 
open as in the figure, and allow the water 
which fills the barrel to pass through them. 
When the bucket arrives at the bottom of 
the barrel, it is drawn up again ; and as the 
valves shut, and prevent the water from re- 
turning through the bucket, it lifts all the 
water contained in the barrel into the cis- 
tern B. At the same time the bucket, in 
rising, makes a vacuum beneath it: the pres- 
sure of the atmosphere upon the surface of 
the water in the well, causes it to mount up 
through the pipe E, open the valves aa, and 
fill the barrel AA. When the bucket begins 
to descend, the column of water beneath it 
descends also, till it is stopped by the shut- 
519 
ting of the valves aa\ the valves bb then 
open, and allow the water to pass through 
as before. 
tig. 2 is a forcing-pump. In this the bar- 
rel AA is screwed upon a square box BB, 
which lias a pair of valves aa at the top of 
the pipe C, bringing water Irom the w ell ; 
and another similar pair at the lower end of 
the pipe D, which is likewise screwed to tire 
square box. The plunger E is solid: when 
it is drawn up it makes a vacuum in the bar- 
rel, and draws the water up through tire 
valves aa trom the well to rill the barrel. 
I he plunger is then forced down, the valves aa 
shut, and as the water has no other way out of 
the box, it passes through bb up the pipe i). 
1 he plunger is then drawn up, the valves bb 
shut, and aa open to supply the barrel as 
before. 
Fig. 3 is a lift-pump. The barrel AA is 
screwed by its top to a shorter barrel II, 
from which the crooked pipe B proceeds. 
A cover /* is screwed over, the top of the bar- 
rel Ii, with a stuffing-box in the middle of 
it ; which is a box containing cotton, or other 
light substances, through which the piston-rod 
E passes. The piston F has two valves bb 
in it, similar to fig. 1 ; and at the bottom of 
the barrel are two valves similar to aa (fig. 
1). When the piston descends, the lower 
valves prevent the water from going outof the 
barrel: and the valves bb open, to let the 
water press through them. When 'the piston 
returns, the valves in it shut, and it raises 
the water through the pipeB; the stuffing-box 
preventing its getting out at the top of the 
barrel, by the side of the piston-rod, as in fig. 
I ; and at the same time, by making a vacu- 
um beneath it, filling, the barrel through the 
lower valves in the same manner as the suck- 
ing-pump. The piston then descends, the 
lower valves shut, and bb open as before. In 
all the figures, W represents a hole in the 
bottom of the pump, to get at the valves to 
repair them ; and when the pump is at work, 
a cover is screwed over it, as shewn in fig. 3. 
Pumps constructed as in the drawing are 
seldom less than one or two feet in the bore 
of the barrel. 
The common sucking-pump may, by a 
small addition, be converted into a lifting- 
pump, fitted for propelling the water to any 
distance, and with any velocity. Fig. 4, is a 
sucking-pump on a small scale, whose work- 
ing-barrel AB has a lateral pipe C, connect- 
ed with it close to the top. This terminates 
in a main or rising pipe, furnished or not 
with a valve, the top of the working-barrel 
AB is shut by a strong plate, having a hollow 
neck terminating in a small tianch. The 
piston-rod passes through this neck, and is 
nicely turned, and polished. A number of 
rings of leather^ are put over the rod, and 
strongly compressed round it by another 
tianch and several screwed bolts. By this 
contrivance, the rod is closely grasped by 
the leathers ; but may be easily drawn up and 
down, while all passage of air or water is ef- 
fectually prevented. The piston is perfo- 
rated, and furnished with a valve opening 
upwards. There is also a valve, T, on the 
top of the suction-pipe; and it will be of 
advantage, though not absolutely necessary, 
to put a valve L at the bottom of the rising- 
pipe. Now, suppose the piston at the bot- 
tom of the working-barrel ; when it is drawn 
up, it tends to compress tire air above it, be- 
