Pulo

they were welcomed by the natives with much urbanity 11 of manners, and conducted to the house of their chief. Pulpitum. Their dress consisted chiefly of blue cotton garments hanging loosely about them; and their flat faces and noses seemed to denote that they were descended from the Chinese. A missionary being of the party, could not understand their language as they spoke it; but as soon as committed to writing it was perfectly intelligible to him. This led to the conclusion, that the inhabitants of Pulo-Condore were originally Cochin Chinese, who fled from their own country in consequence of their attachment to one of its sovereigns who had been dethroned by a number of his own subjects.

Here the squadron was to purchase provisions, aud the people promised to have the proposed quantity in readiness, if possible, at the appointed time. Next morning, a party of pleasure went from the Hindostan to a small island near Pulo-Condore; but being apprehensive of an approaching storm, they made towards the ship with all convenient speed. The weather again becoming favourable, they set off for the island again, and were astonished, on their arrival, to find it wholly abandoned. In the principal cabin a letter was found, written in the Chinese language, expressing their terror at the arrival of such great ships and powerful persons; not being able to satisfy their demands as to cattle and other provisions, the poor inhabitants of Pulo-Condore having scarcely any to supply, they therefore fled to preserve their lives; declared themselves to be few in number, and very poor, but honest; and concluded with requesting the great people to have pity on them, as they had left their all behind, and earnestly implored them not to burn their cabins.

The generous English left them an intimation that they called merely for refreshment on fair and equitable terms, without harbouring against them any evil designs. They claimed a connection to a civilized nation, actuated by principles of humanity, by which they were prohibited from plundering or doing injury to others, who might have the misfortune to be fewer or weaker than themselves. No doubt the poor terrified inhabitants would be agreeably surprised to find, on their re turn, not only that all their tents were in perfect safety, but that nothing was either disturbed or removed, and a small present left to their chief in the principal dwelling. PULO-Lingen, another island of the cluster mentioned above, is of some extent, though inferior in size to Pulo-Condore. It is chiefly remarkable for a mountain in its centre, terminating in a fork like Parnassus, but denominated by mariners the asses ears. The people of Lord Macartney's squadron were constantly discovering new islands, many of which were clothed with verdure; some had lofty trees growing upon them; others were nothing but naked rocks, the resort of innumerable birds, and whitened with their dung.

PULO PENANG. See PRINCE of Wales's Island. PULP, in Pharmacy, the fleshy and succulent parts of fruits extracted by infusion or boiling, and passed through a sieve.

PULPIT, an elevated place in a church, whence sermons are delivered. The French give the same name to a reading desk.

PULPITUM, in the Grecian and Roman theatres, was a place where the players performed their parts. It was lower than the scena, and higher than the orchestra.

PULSE, in the animal economy, denotes the beating or throbbing of the heart and arteries.

No doctrine has been involved in more difficulties than that of pulses; since, in giving a physiological account of them, physicians have espoused quite opposite sentiments; whilst some doubt whether the pulse is owing to the systole or diastole; as also, whether the motion of the heart and arteries is one and the same, for a moment of time.

:

With regard to motion, the pulses are reckoned only four; great and little, quick and slow. When quickness and greatness are joined together, it becomes violent; and when it is little and slow it is called a weak pulse. They are also said to be frequent and rare, equal and unequal; but these are not the essential affections of motion. Frequency and quickness are often confounded with each other. A pulse is said to be hard or soft, with regard to the artery, according as it is tense, renitent, and hard, or flaccid, soft, and lax for the disposition of the arteries contributes greatly to the change of the pulse; wherefore it sometimes happens, that the pulse in both arms is not alike, which is very common in a hemiplexy. Add to these a convulsive pulse, which does not proceed from the blood, but from the state of the artery; and is known by a tremulous subsultory motion, and the artery seems to be drawn upwards: this, in acute fevers, is the sign of death; and is said to be the pulse in dying persons, which is likewise generally unequal and intermitting. A great pulse shows a more copious afflux of the blood to the heart, and from thence into the arteries: a little pulse the contrary.

The pulses of persons differ according to the largeness of the heart and vessels, the quantity and temperies of the blood, the elastic force of the canals; as also with regard to the sex, age, season, air, motion, food, sleep, watchings, and passions of the mind. The pulse is larger and more quick in men than in women; in the bilious and sanguineo-bilious, than in the phlegmatic and melancholic. Those who are lean, with tense fibres, and large vessels, have a greater and a stronger pulse, than those that are obese, with lax fibres and small vessels; whence they are more healthy, robust, and apt for labour. In children, the pulse is quick and soft; in adults greater and more violent. In the old, it is commonly great, hard, and slow. Labour, motion, and exercise of the body, increase the circulation of the blood, the excretions, and particularly respiration; rest renders the circulation slow and weak; intense speaking increases the circulation, and consequently renders the pulse large and quick. In watching, the pulse is more evident; in sleep, more slow and languid. After drinking hot things, such as coffee and tea, or hot bath-waters, as well as after meals, the pulse vibrates more quick. But nothing produces a greater change in the pulse than affections of the mind: in terror, it is unequal, small, and contracted: in joy, frequent and great; in anger, quick and hard; in sadness, slow, small, deep, and weak; and in intense study, languid and weak. With regard to the air, when, after the predominancy

Pulse, predominancy of a west or south wind, it becomes north Pulteney or east, the pulse is stronger and larger ;_ as also when the quicksilver rises in the barometer. But when the atmosphere is dense, humid, rainy, with a long south wind as also where the life is sedentary, the sleep long, and the season autumnal, the pulse is languid and small, and the perspiration decreased. In May it is great, and sometimes violent; in the middle of summer, quick but weak; in the autumn, slow, soft, and weak; in the winter, hard and great. A drastic purge and an emetic render the pulse hard, quick, and weak, with loss of strength; chalybeates, and the bark, render it great and robust, and the complexion lively; volatiles amplify and increase the pulse; acids and nitrous remedies refrigerate the body, and appease the pulse; opiates and the like render it small and weak, and decrease the elasticity of the solids; and poisons render it small, contracted, and hard. When the quantity of the blood is too great, bleeding raises the pulse.

PULSE, is also used for the stroke with which any medium is affected by the motion of light, sound, &c. through it.

Sir Isaac Newton demonstrates, that the velocities of the pulses in an elastic fluid medium (whose elasticity is proportionable to its density) are in a ratio compounded of half the ratio of the elastic force directly, and half the ratio of the density inversely; so that in a medium whose elasticity is equal to its density, all pulses will be equally swift.

PULSE, in Botany, a term applied to all those grains or seeds which are gathered with the hand; in contradistinction to corn, &c. which are reaped, or mowed: or, It is the seed of the leguminous kind of plants, as beans, vetches, &c.; but is by some used for artichokes, asparagus, &c.

PULTENEY, WILLIAM, the famous opposer of Sir Robert Walpole in parliament, and afterward earl of Bath, was descended from one of the most ancient families in the kingdom, and was born in 1682. Being well qualified in fortune, he early procured a seat in the house of commons, and distinguished himself as a warm partisan against Queen Anne's ministry; whose errors he had sagacity to detect, and spirited eloquence to expose. When King George I. came to the throne, Mr Pulteney was made secretary at war, and soon after cofferer to the king's household; but the good understanding between this gentleman and Sir Robert Walpole, who then acted as prime minister, was interrupted in 1725, on a suspicion that Walpole was desirous of extending the limits of prerogative, and of promoting the interests of Hanover, to the prejudice of those of Britain. His opposition to Sir Robert was indeed carried to such indiscriminate lengths, that some have been of opinion he often acted against measures beneficial to the public, merely from personal motives. It would be impracticable here to trace his parliamentary conduct: 80 it must suffice to observe in general, that he became so obnoxious to the crown, that in 1731 the king called for the council-book, and with his own hand struck out his name from the list of privy-counsellors; a proceed

ing that only served to inflame his resentment and in- Pulteney crease his popularity. Thus he still continued to at- I tack the minister with a severity of eloquence and sar- Pump. casm that worsted every antagonist; so that Sir Robert was heard to declare, he dreaded that man's tongue more than another man's sword. At length, when Walpole found the place of prime minister no longer tenable, and resigned in 1741, among other promotions Mr Pulteney resumed his place in the privy-council, and was created earl of Bath; a title purchased at the expence of that popularity which afterward he naturally enough affected to contemn. In 1760, toward the close of the war, he published A Letter to two Great Men, recommending proper articles to be insisted on in a treaty of peace; which, though the writer was then unknown, was greatly applauded, and went through several impressions. He died in 1764; and as his only son died before him, the title became extinct.

PULVERIZATION, the art of pulverizing, or reducing a dry body into a fine powder; which is performed in friable bodies by pounding or beating them in a mortar, &c; but to pulverize malleable ones, other methods must be taken. To pulverize lead, or tin, the method is this: Rub a round wooden box all over the inside with chalk; pour a little of the melted metal nimbly into the box; when shutting the lid, and shaking the box briskly, the metal will be reduced to powder.

PUMEX, the PUMICE-STONE. See MINERALOGY Index.

Pumice-stone is used in some mechanical arts; as for rubbing and smoothing the surface of metals, wood, pasteboard, and stone; for which it is well fitted by reason of its harsh and brittle texture; thus scouring and carrying off the little inequalities from the surfaces just mentioned.

PUMICE-STONE. See MINERALOGY Index. PUMP, an hydraulic machine for raising water by means of the pressure of the atmosphere.

It would be an entertaining and not an uninstruc-Of the i tive piece of information to learn the progressive steps veution of by which the ingenuity of man has invented the various pumps. 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 restless spirit of the Europeans has discovered, either in the new continent of America, or the islands of the Pacific ocean. Nay, it was unknown in the cultivated empire of China at the time of our arrival there by sea; and it is still a rarity everywhere in Asia, in places unfrequented by the Europeans. It does not appear to have been known to 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 (A). It is perhaps not difficult to trace the steps by which those mechanicians were led

to

Pump.

'Plate

pump.

2

NORIA.

In

Pama

early, it is not improbable that the common pump sketched in fig. 3. was as old as that of Ctesibius. this place we shall first give a short description of the ig. 3. chief varieties of these engines, considering them in their simplest form, and we shall explain in very general terms their mode of operation. We shall then give a concise and popular theory of their operation, furnishing principles to direct us in their construction; and we shall conclude with the description of a few peculiarities which may contribute to their improvement or perfection.

to the invention. The Egyptian wheel was a common machine all over Asia, and is still in use in the remotest corners, and was brought by the Saracens into Spain, where it is still very common under its ancient name The Danish missionaries found in a remote village in the kingdom of Siam the immediate off-spring of the noria (Lettres Edifiantes et Curieuses). It was a wheel turned by an ass, and carrying round, not a string of earthen pots, but a string of wisps of hay, which it drew through a wooden trunk. This rude chain-pump was in frequent use for watering the rice fields. It is highly probably that it is of great antiquity, although we do not recollect its being mentioned by any of the Greek or Roman writers. The Arabs and Indians were nothing less than innovators; and we may suppose with great safety, that what arts we now find among them they possessed in very remote periods. Now the step from this to the pump is but short, though it is nice and refined; and the forcing pump of Ctesibius is

the easiest and most natural.

Let AB (fig. 1.) be the surface of the water in the CCCCXLIX. well, and D the height where it is to be delivered. Let fig. 1. DC be a long wooden trunk, reaching as deep under Ctesibius's water as possible. Let the rope EF be fitted with its knot of hay F. When it is drawn up through the trunk, it will bring up along with it all the water lying between C and A, which will begin to run out by the spout D as soon as the knot gets to G, as far below D as C is below A. All this is very obvious: and it required but little reflection to be assured, that if F was let down again, or pushed down, by a rod instead of a rope, it would again perform the same office. Here is a very simple pump. And if it was ever put in practice, it behoved to show the supporting power of the atmosphere, because the water would not only be lifted by the knot, but would even follow it. The imperfection of this pump behoved to appear at first sight, and to suggest its remedy. By pushing down the knot F, which we shall henceforth call the piston, all the force expended in lifting up the water between A and G is thrown away, because it is again let down. A valve G, at the bottom would pervent this. But then there must be a passage made for the water by a lateral tube KBD (fig. 2.) And if this be also furnished with a valve H, to prevent its losing the water, we have the pump of Ctesibius, as sketched in fig. 2. The valve is the great refinement: but perhaps even this had made its appearance before in the noria. For, in the more perfect kinds of these machines, the pots have a stop or valve in their bottom, which hangs open while the pot descends with its mouth downwards, and then allows it to fill readily in the cistern: whereas, without the valve, it would occasion a double load to the wheel. If we suppose that the valve had made its appearance so

Fig. 2.

There are but two sorts of pumps which essentially differ; and all the varieties that we see are only modi. fications of these. One of these original pumps has 2 solid piston; the other has a piston with a perforation and a valve. We usually call the first a FORCING PUMP, and the second a LIFTING or SUCKING PUMP.

Fig. 2.

Fig. 2. is a sketch of the forcing pump in its most Forcing simple form and situation. It consists of a hollow cylin-pump deder AC c a, called the WORKING BARREL, open at both scribed. ends, and having a valve G at the bottom, opening upwards. This cylinder is filled by a solid piston EF, covered externally with leather or tow, by which means it fits the box of the cylinder exactly, and allows no water to escape by its sides. There is a pipe KHD, which communicates laterally with this cylinder, and has a valve at some convenient place H, as near as possible to its junction with the cylinder. This valve also opens upwards. This pipe, usually called the RISING PIPE, or MAIN, terminates at the place D, where the water must be delivered.

This

4

Now suppose this apparatus set into the water, so Its mode of that the upper end of the cylinder may be under or even operation. with the surface of the water AB; the water will open the valve G, and after filling the barrel and lateral pipe, will also open the valve H, and at last stand at an equal height within and without. Now let the piston be put in at the top of the working barrel, and thrust down to K. It will push the water before it. will shut the valve G, and the water will make its way through the valve H, and fill a part B b of the rising pipe, equal to the internal capacity of the working barrel. When this downward motion of the piston ceases, the valve H will fall down by its own weight and shut this passage. Now let the piston be drawn up again: The valve H hinders the water in the rising pipe from returning into the working barrel. But now the valve G is opened by the pressure of the external water, and the water enters and fills the cylinder as the piston rises. When the piston has got to the top, let it be thrust down again: The valve G will again be shut, and the water will be forced through the passage at H, and rise along the main, pushing before it the water already there, and will now have its surface at L. Repeating this operation, the water must at last arrive at D, how

ever

Pump.

Lifting pump.

ever remote, and the next stroke would raise it to e; so that during the next rise of the piston the water in e D will be running off by the spout.

The effect is the same whatever be the position of the working barrel, provided only that it be under water. It may lie horizontally or sloping, or it may be with its mouth and piston rod undermost. It is still the same forcing pump, and operates in the same manner and by the same means, viz. the pressure of the surrounding water.

The external force which must be applied to produce this effect is opposed by the pressure exerted by the water on the opposite face of the piston. It is evident, from the common laws of hydrostatics, that this opposing pressure is equal to the weight of a pillar of water, having the face of the piston for its base, and the perpendicular height d A of the place of delivery above the surface of the water AB in the cistern for its height. The form and dimensions of the rising pipe are indifferent in this respect, because heavy fluids press only in the proportion of their perpendicular height. Observe that it is not d F, but d A, which measures this pressure, which the moving force must balance and surmount. The whole pressure on the under surface Ff of the piston is indeed equal to the weight of the pillar d Fƒð; but part of this is balanced by the water AFfa. If indeed the water does not get into the upper part of the working barrel, this compensation does not obtain. While we draw up the piston, this pressure is removed, because all communication is cut off by the valve H, which now bears the whole pressure of the water in the main. Nay, the ascent of the piston is even assisted by the pressure of the surrounding water. It is only during the descent of the piston therefore that the external force is necessary. Observe that the measure now given of the external force is only what is necessary for balancing the pressure of the water in the rising pipe. But in order that the pump may perform work, it must surmount this pressure, and cause the water to issue at D with such a velocity that the required quantity of water may be delivered in a given time. This requires force, even although there were no opposing pressure; which would be the case if the main were horizontal. The water fills it, but it is at rest. In order that a gallon, for instance, may be delivered in a second, the whole water in the horizontal main must be put in motion with a certain velocity. This requires force. We must therefore always distinguish between the state of equilibrium and the state of actual working. It is the equilibrium only that we consider at present; and no more is necessary for understanding the operation of the different species of pumps. The other force is of much more intricate investigation, and will be considered by itself.

The simplest form and situation of the lifting pump is represented by the sketch fig. 3. The pump is im mersed in the cistern till both the valve G and piston F are under the surface AB of the surrounding water. By this means the water enters the pump, opening both valves, and finally stands on a level within and without. Now draw up the piston to the surface A. It must operating. lift up the water which is above it (because the valve in the piston remains shut by its own weight); so that its surface will now be at a, A a being made equal to AF. In the mean time, the pressure of the surrounding water forces it into the working barrel, through the valve G;

Its mode of

and the barrel is now filled with water. Now, let the piston be pushed down again; the valve G immediately shuts by its own weight, and in opposition to the endeavours which the water in the barrel makes to escape this way. This attempt to compress the water in the barrel causes it to open the valve F in the piston; or rather, this valve yields to our endeavour to push the piston down through the water in the working barrel. By this means we get the piston to the bottom of the barrel; and it has now above it the whole pillar of water reaching to the height a. Drawing up the piston to the surface A a second time, must lift this double column along with it, and its surface now will be at b. The piston may again be thrust down through the water in the barrel, and again drawn up to the surface; which will raise the water to c. Another repetition will raise it to d; and it will now show itself at the intended place of delivery. Another repetition will raise it to e; and while the piston is now descending to make another stroke, the water in e d will be running off through the spout D; and thus a stream will be produced, in some degree continual, but very unequal. This is inconvenient in many cases: thus, in a pump for domestic uses, such a hobbling stream would make it very troublesome to fill a bucket. It is therefore usual to terminate the main by a cistern LMNO, and to make the spout small. By this means the water brought up by the successive strokes of the piston rises to such a height in this cistern, as to produce an efflux by the spout nearly equable. The smaller we make the spout D the more equable will be the stream; for when the piston brings up more water than can be discharged during its descent, some of it remains in the cistern. This, added to the supply of next stroke, makes the water rise higher in the cistern than it did by the preceding stroke. This will cause the efflux to be quicker during the descent of the piston, but perhaps not yet sufficiently quick to discharge the whole supply. It therefore rises higher next stroke; and at last it rises so high, that the increased velocity of efflux makes the discharge precisely balance the supply. Now, the quantity supplied in each stroke is the same, and occupies the same room in the cistern at top; and the surface will sink the same number of inches during the descent of the piston, whether that surface bas been high or low at the beginning. But because the velocities of the efflux are as the square roots of the heights of the water above the spout, it is evident that a sink of two or three inches will make a smaller change in the velocity of efflux when this height and velocity are great. This seems but a trifling observation; but it serves to illustrate a thing to be considered afterwards, which is important and abstruse, but perfectly similar to this.

It is evident, that the force necessary for this operation must be equal to the weight of the pillar of water dA a D, if the pipe be perpendicular. If the pump be standing aslope, the pressure which is to be balanced is still equal to the weight of a pillar of water of this perpendicular height, and having the surface of the piston for its base.

Such is the simplest, and, we may add, by far the best, form of the forcing and lifting pumps; but it is not the most usual. Circumstances of convenience, economy, and more frequently of fancy and habit, have caused the pump-makers to deviate greatly from this form. It is not usual to have the working barrel in

Effect of giving the piston a longer stroke

8

inconvenient and unneces sary.

9

Effect of

the weight

of the water and

pressure of the atmosphere.

We have supposed, in our account of the lifting pump, that the rise of the piston always terminated at the surface of the water in the cistern. This we did in order that the barrel might always be filled by the pressure of the surrounding water. But let us suppose that the rise of the piston does not end here, and that it is gradually drawn up to the very top: it is plain that the pressure of the atmosphere is by this means taken off from the water in the pipe (see PNEUMATICS), while it remains pressing on the water of the cistern. It will therefore cause the water to follow the piston as it rises through the pipe, and it will raise it in this way 33 feet at a medium. If, therefore, the spout D is not more than 33 feet above the surface of the water in the cistern, the pipe will be full of water when the piston is at D. Let it be pushed down to the bottom; the water will remain in the pipe, because the valve G will shut and thus we may give the piston a stroke of any length not exceeding 33 feet. If we raise it higher than this, the water will not follow; but it will remain in the pipe, to be lifted by the piston, after it has been pushed down through it to the bottom.

But it is not necessary, and would be very inconvenient, to give the piston so long a stroke. The great use of a pump is to render effectual the reciprocation of a short stroke which we can command, while such a long stroke is generally out of our power. Suppose that the piston is pushed down only to b; it will then have a column bf incumbent on it, and it will lift this column when again drawn up. And this operation may be repeated like the former, when the piston was always under water; for the pressure of the atmosphere will always cause the water to follow the piston to the height of 33 feet.

Nor is it necessary that the fixed valve G be placed at the lower orifice of the pipe, nor even under water. For, while things are in the state now described, the piston drawn up to f, and the whole pipe full of water; if we suppose another valve placed at b above the surface of the cistern, this valve can do no harm. Now let the piston descend, both valves G and 6 will shut. G may now be removed, and the water will remain supported in the space bG by the air; and now the alternate motions of the piston will produce the same effect as before.

We found in the former case that the piston was carrying a load equal to the weight of a pillar of water of the height AD, because the surrounding water could only support it at its own level. Let us see what change is produced by the assistance of the pressure of the atmosphere. Let the under surface of the piston be at b; when the piston was at f, 33 feet above the surface of the cistern, the water was raised to that height by the pressure of the atmosphere. Suppose a partition made at b by a thin plate, and all the water above it taken away. Now piece a hole in this plate. The pressure of the atmosphere was able to carry the whole column fa. Part of this column is now removed, and the remainder is not a balance for the air's pressure. This will therefore cause the water to spout up through this hole and rise to f. Therefore the under surface of this

plate is pressed up by the contiguous water with a force Pump. equal to the weight of that pillar of water which it formerly supported; that is, with a force equal to the weight of the pillar fb. Now the under surface of the piston, when at b, is in the same situation. It is pressed upwards by the water below it, with a force equal to the weight of the column fb: But it is pressed downwards by the whole pressure of the atmosphere, which presses on all bodies; that is, with the weight of the pillar fa. On the whole, therefore, it is pressed downwards by a force equal to the difference of the weights of the pillars fa and fb; that is, by a force equal to the weight of the pillar ba.

It may be conceived better perhaps in this way.. When the piston was under the surface of the water in the cistern, it was equally pressed on both sides, both by the water and atmosphere. The atmosphere exerted its pressure on it by the intervention of the water; which being, to all sense, a perfect fluid, propagates every external pressure undiminished. When the piston is drawn up above the surface of the pit-water, the atmosphere continues to press on its upper surface with its whole weight, through the intervention of the water which lies above it; and its pressure must therefore be added to that of the incumbent water. It also continues to press on the under surface of the piston by the intervention of the water; that is, it presses this water to the piston. But, in doing this, it carries the weight of this water which it is pressing on the piston. The pressure on the piston therefore is only the excess of the whole pressure of the atmosphere above the weight of the column of water which it is supporting. Therefore the difference of atmospheric pressure on the upper and under surfaces of the piston is precisely equal to the weight of the column of water supported in the pipe by the air. It is not, however, the individual weight of this column that loads the piston; it is the part of the pressure of the atmosphere on its upper surface, which is not balanced by its pressure on the under surface.

In attempting, therefore, to draw up the piston, we have to surmount this unbalanced part of the pressure of the atmosphere, and also the weight of the water which lies above the piston, and must be lifted by it: and thus the whole opposing pressure is the same as before, namely, the weight of the whole vertical pillar reaching from the surface of the water in the cistern to the place of delivery. Part of this weight is immediately carried by the pressure of the atmosphere; but, in lieu of it, there is an equal part of this pressure of the atmosphere abstracted from the under surface of the piston, while its upper surface sustains its whole pressure.

ΤΟ

So far, then, these two states of the pump agree. Other cirBut they differ exceedingly in their mode of operation; cumstances and there are some circumstances not very obvious which to be atmust be attended to, in order that the pump may deli- tended to. ver any water at the spout D. This requires, therefore, a serious examination.

Let the fixed value G (fig. 4.) be supposed at the Fig. 4. surface of the cistern water. Let Mm be the lowest, and Nn the highest, positions of the piston, and let HA=h be the height of a column of water equiponderant with the atmosphere.

When the pump is filled, not with water, but with air, and the piston is in its lowest position, and all in equilibrio, the internal air has the same density and 3 R2 elasticity