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50.

at a bladder cut of by ye two ends or by some other means;  that part of ye finger would be swelled extremely, and there would be felt much pain;  whence it follows that part of ye finger wch stops ye [[?appercorifice]] of ye pipe of ye Barometer being contiguous to ye much dilated air and ye rest being pressed by all ye weight of ye atmosphere, that small part ought to be blown and make a great convexity towards ye interior part of ye pipe, wch cannot be made without pain;  and ye more ye air shall be rarefied in ye pipe ye more that puffing up and pain shall be sensible, and ye feels ye pushing back of that rarefied air shall not be sufficient to hinder that puffing up of ye end of ye finger, since ye rest wch is in ye full air is much more pressed.

It may be objected that when there is 28 inches of mercury suspended in ye peipe, if we lift it up without puting it out of ye mercury, ye vessel feels of an equal weight to that of ye inclosed mercury wch ought not to happen if it made an equilibrium with ye weight of ye atmosphere.  We may answer to that diffulty by saying that ye superior air wch is above ye pipe hath not then any other air to make an equilibrium with;  for that wch ought to sustain it at ye bottom of ye pipe, sustains ye mercury wch is there;  wherefore it ought to sustain ye whole weight of ye superior air wch weighs 28 inches of mercury; and if ye pipe was but 14 inches and that ye mercury remained at ye height then we should feel but 14 inches of mercury in weight, because that ye air wch is sufficated upon ye mercury of ye small vessel wold sustain there 14 inches, and would make an effort of 14 inches towards ye top of ye pipe inwardly:  so that it would make an equilibrium with half ye weight of ye superior air and ye hand would sustain ye rest.

  The flame can make also an equilibrium by its spring with ye other bodys;  but as there is none but ye flame of gunpowder wch can indure to be compressed without being extinguished, and that flame endures but a very small time, it is difficult to make experiements of its equilibrium, and ye force of its spring is so great, that we cannot yet find as weight so great that it doth not surmount since it will overturn entire bastions and also mountains.

  To understand how it makes so great an effort, we may suppose that there is a certain quantity of lighted powder wch fills a pipe sufficiently large situated perpendicularly and that a great weight whose bigness occupys and fills up precisely that of ye pipe in pressing ye flame of ye powder, makes it be constracted till being reduced to a small space where is made an equilibrium between ye weight and ye spring of ye flame without quenching it;  wch we may conceive to make during ye space of one second, and in that estate ye spring of ye flame should make an equilibrium with ye weight so that if ye weight was augmented ye flame would be reduced to a little less space, supposing it doth not extinguish it;  and it spring wch would then be more strong would make yet an equilibrium with that great weight.  Now if we conceive that in that moment there is lighted some quantity of new powder ye spring of ye flame shall be augmented, and ye weight not being able to make an equilibrium shall be pushed on heigh, and being once in motion ye continuation of ye extention of ye spring of ye flame wch will display itself and be extended more and more, will more and more accelerate its motion, and at last will push it very heigh into ye air.

  This being supposed it is easy to conceive that if we put 10 or 12000 of powder in a mine;  and that all that powder being lighted may, posses a space of 200 feet heigh and 100 feet large, it will happen that there will be lighted at ye begining a small quantity wch shall not be sufficient to overthrow ye Baston:  but because that ^[[that]] flame hath this property not to be extingished by being pressed, it shall light 30 or 40 times more than that wch would posses ye chamber of ye mine if it was uncovered;  and then its spring is strong enough it will begin to elevate ye earth wch is above wch being once in motion and ye rest of ye powder continueth to enflame and fills ye space that ye earth [[strikethrough]] ye [[/strikethrough]] hath quitted in begining to be elevated, so that its spring may be yet greater than ye weight of ye earth wch is allready in motion, it will accelerate its motion more and more and at last blow up ye Bastion or at least one part, till all ye flame math acquired ye extent wch is nature to it in ye free air:

A little powder produceth ye same effects in cannons;  for it is lighted successively (althô in a little time) without pushing out ye bullet till ye spring of ye pressed flame surmounts ye resistance of ye bullet;  and when it begins to move ye rest of ye powder wch is readily lighted;  augments its spring and accelerates ye swiftness of ye bullet till it is pushed to 7 or 800 toises:

  Whence we may see that a cannon of 20 feet ought to carry it bullet further than one of 10 feet because that ye powder hath more time to be lighted and augment its spring while ye bullet runs these spaces:

  may see also that if a quantity of powder lighted hath ye force to shake a bullet wch is not well joyned to ye cannon, it shall not pass so far as if it had been well [[?bred]] and pressed with cork or other things wch may hinder its being [[?put]] in motion till there is 2 or 3 times that quantity of powder lighted:  for in this last case ye begining at its motion shall be swifter and its acceleration greater.

  For ye same reason ye powder being very fine and easy to be enflamed shall push ye bullet further than if it was more gross, because it is more lighted while ye bullet is in ye cannon.
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Transcription Notes:
mandc: 1 Toise was exactly 6 pieds (feet) (about 1.949 metres) in France until 1812