A Demonstration of the Velocity wherwith the Air rushes into an Exhausted Receiver lately produced before the R.Society by Dr. D. Papin Reg. Soc. S. There being severall occasions wherein it would be usefull to Know the velocity of the Air according to the severall pressures that may drive it: the Royall Academy at Paris hath attemp ted by some tryalls to attain that Knowledge and by means of a bladder which they did some times fill up with water and some times with Air; they found that (although the weight to squeeze out these liquors, and the hole to let them out were the same) nevertheless the bladder when full of Air, could be empty’d in the 25th part of the time that was required to squeeze out the water out of the same bladder: from thence they concluded that the swifteness of the Air is 25 times greater then that of water when both these liquor’s bear the same pressure. This experiment was very well thought on, and might serve <s>whilst people should look for some thing better <\s> till a better should be found out but, sure, these gentlemen knew well enough that this was not perfect: the reason is that the Air yieldeth much and so the bladder being fill’d with it, will become pretty flatt, as soon as a considerable weight is lay’d upon it: it is plain therefore that the weight bearing upon a large space doth not press every part with the same force as it would do if the bladder did for a while remain plump as it doth when full of water: more over, the water itself being heavy in the bladder mak’s some pressure: so that it appears that the pressure in this experiment was not quite so great upon the Air as upon the water: I have therefore thought of another way which I think better, to come to the say’d knowledge and I do humbly submit it to the R. Society. My way is grounded upon this <u>Hydrostatical Principle <\u>, that <u>liquors have a strength to ascend as high as their <s>Spring <\s> source is <\u> and although the resistence of the <u>Medium <\u> doth always hinder <s>the Jettes <\s> Jects d’eau in the open Air from reaching quite so high, nevertheless the liquor at its first spouting out, hath the necessary swift ness to come to that heigth.
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Of the Velocity of Air passing into an Exhausted receiver by Denis Papin, 1686. From The Royal Society, CLP/18i/35
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