The Answer of Dr. Papin to Several Objections Made by Mr. Nuis against His Engine for Raising Water by the Rarefaction of the Air, Whereof a Description is Given in No. 178. of These Transactions

The Answer of Dr. Papin to several Objections made by Mr. Nuis against his Engine for raising Water by the rarefaction of the Air, whereof a description is given in No. 178. of these Transactions. Having seen in the Nouvelles de la Republ. des Lettres of the Month of December last, some difficulties which Mr. Nuis doth find in my new way for raising Water, publish't in the Philosophical Transactions of the month of January; I am obliged to answer them as clearly as I can in these short notes. In his first Objection he saith, that it would be a very hard matter to hinder but some Receptracles would come to be fill'd too much: So that the water filling also the pipes C D D would hinder the effect of the Engin. To this I answer that it being necessary to let out the water of the highest Receptracle, I thought it might be conceived that the water may also be let out of the inferior Receptracles by inserting into each of them a crooked pipe, reaching a pretty way downwards, and having its lower aperture shut up with a valve; whereby the water might run out when the Receptracle should be fill'd to a certain height: and so I did not judge it needfull to prevent this Objection. The second Difficulty, which I had very well foreseen (as it is plain in my first explication) lies in the great quantity of Air to be rarefied: So that Mr. Nuis, by his computation, doth find that the Pump's should every one contain, 84 cubick feet of rarefied Air to raise water at 1200 foot distance. To this I may answer, first that I have not positively promised a good success but for Windsor and St.Germain; but when I spoke of Versailles I used the word perhaps, thereby shewing that before any one should go about such a great undertaking he should reflect upon it it more than I would then do, not having occasion for such work: but since I have seen Mr. Nuis his Objection, I have been Obliged in order to answer him to make the following computation. Let the distance as he supposeth be 12000 foot, and the Capacity of each Receptacle be about one half of a cubick foot: I might make the wheel with the Axis to make their revolution in one minute of time, and so order all things that the Air under the ascending plugs might come to be rarefied to such a degree, that by its Elasticity it might not counterpoise more than 7 foot of water: but at the same time the Air in the Receptacles A A, B B, would even in it's greatest dilatation be able to counterpoise 17 foot: so it is plain that the Air will be driven from the Receptacles into the Pumps by a strength equivalent to ten foot of water: Now if we compute after the method publish'd in the Transaction of the month of October last, what should be the Velocity of the Air driven by such a pressure: we shall find that the said Velocity will be about 740 foot in a second: So that in half a minute, during which the plug goeth up, this Air might pass above 22000 foot, although it were not rarif'd at all; but being rarif'd, as we do suppose it to be, it might go a great deal further. I must now take notice that according to the Honourable Mr. Boile's Experiments quoted by Mr. Nuis, the Rarefaction of the Air is much lesser than he takes it to be: For the Water contain'd in the Pipe N O. is so far from causing the Air to fill up a space four times bigger, that it will not extend itself to a space once bigger than before; considering therefore the Velocity of the Air and the small dilatation it doth suffer, if any one will take the trouble to compute, he will find that if the Pumps have in Diameter the Diagonal of a Square Foot, and the same height: and if the small Tubes of communication be made of \( \frac{1}{3} \) part of an Inch in Diameter, so that being 12000 Foot long, they may contain about one cubick Foot of Air: Air, that would be more than sufficient to make the necessary Rarefaction in the Receptacles: And thus much might answer Mr. Nuis his Objection. But for the good success of the Engine it is not enough to make the Air pass from the Receptacles into the Pumps, it must also return from the Pumps into the Receptacles: Now for this intent it would be necessary to set the Receptacles but five Foot above one another; so to drive the Water up the Pipe NO, it would be enough that the Air in the Receptacle B should press with a strength equivalent to 23 Foot of Water: For it is plain that 5 Foot in the Pipe NO, together with a pressure equivalent to 17 Foot which I have supposed to be in the upper Receptacle A, will make but 22 Foot in all: and therefore 23 Foot pressing in the Receptacle B must prevail and cause the Water to ascend: now the pressure in the Receptacle being but 23 Foot, and the Air in the Pump returning to its ordinary pressure, which is about 33 Foot; it is plain that the Air going back to the Receptacle will be driven by a strength equivalent to 10 Foot, as well as it had been in coming from the Receptacle towards the Pump: and so the bigness assigned for the communication-Pipes will also prove more than sufficient to this effect. From what I have been saying it is plain, that in great distances there should be made as many Pumps as Receptacles, as I had propounded in the first explication of my Engine: and for to raise Water but 60 Foot high, there should be required 13 or 14 Receptacles and as many Pumps of the bigness aforesaid. Some people may take this for a great difficulty. But I answer that in this Engine this is not so much as it seems at first; because the pressure being all from without, there is no need of any great strength to resist it, and so the Metal for the Pumps will cost but little: there may also be found occasions where to make so good use of them, that such an Engine as I have described would in a years time save labour enough to pay for for many Pumps, since it might every hour raise about 1800 pounds of Water to the height of 60 Foot: Meanwhile I don't pretend to have given here the best proportion for the bigness of every part of the Engine; but it may be, by altering the Capacity of the Pumps, of the Pipes, or of the Receptacles, a much more considerable effect might be produced: but I'lle leave this to be looked after by those that may have occasion for it; and for my part I content myself having shewn the truth of what I had at first, though but doubtfully, propounded: For the River Seine, where it is nearest to Versailles, not being above 20000 Foot distant, it is easy to see that, to supply this increase of distance, we might lessen at pleasure the capacity of the Receptacles, or increase the capacity of the Pumps and of the Pipes, or cause the wheel to spend more time in its revolution: 'tis true the Engine would produce less effect, but upon a great River the number of the Engines might be multiplied, and vast quantities of Water still be raised. I shall therefore, to prevent new difficulties, add only this: that as well as in the Receptacles I have a way to prevent the overflowing with Water; so in the Pumps I might also prevent the overfilling with Air, by making a Valve that should open as soon as the Air in the Pump should be more compress than the outward Air: So the Air getting in through any pores would constantly be let out. As for the third objection wherein Mr. Nui says that it doth not appear how the Water in our Engine may, by Rarefaction, ascend higher than 32 Foot. I answer that the Water doth not at any time ascend higher than from a lower Receptacle into the next upper Receptacle, which height is but 12 Foot: So that it is plain enough that the pressure of the Air may be sufficient to drive it up. It is indifferent whether it be by Rarefaction or otherwise that the Water comes into the Receptacle A; it is enough that the Water is there, and that the Air presses upon upon it with such a strength as will prevail against all that opposeth it, as I have shewn above. To the fourth Difficulty I answer: That although the use of the Pipes be meerly for the conveying of Air: They may nevertheless easily be fill'd with Water when need requires, and so the defects in them may as well be found out as in the Pipes that are used for the conveying of Water. This is all I may answer at present, and I shall make an end with assuring Mr. Nuis that i'le make use of his advice when ever he will be pleased to give it me. An answer of the same to the Author of the perpetual Motion. In the last papers I published in Phil. Transact. N. 184 against this perpetual Motion described in N. 177. I intreated the Author to permit me to say nothing as to what alterations he might make in his Engine; resolving to leave it to others to shew him that upon that principle all he can do signifies nothing. But I find since, in the Nouvelles de la Republ: for December last, that he still persists to urge some new contrivances, which being added he conceives his Engine must succeed. To this I answer that I undertook only to shew that his first device would faile, which yet I should scarce have done, if I had thought a dispute of this nature could have lasted so long. To come therefore to the point, where he faith that this Engine may well succeed without alteration, because he hath tryed with Liquors put into Bellows immersed in Water: I again say that I grant him the truth of the Experiments, but deny the consequences he would draw