606 PHILOSOPHICAL TEANSACTIONS. [aNNO I67I, 



stitutions, (of Tuscany for instance) and proposes a way of explaining the 

 phcEnomena of the general deluge, not contradicting the laws of natural 

 motions. 



The Co7npressio?i of Air hy Water. N" 7^, p- 2192. 



Some members of the Royal Society, with two diiFerent sorts of instruments, 

 made experiments for finding the proportions of the compression of air, by or 

 under water, in the month of July, at Sheerness, in the mouth of the river 

 Medway, at the time of high water, where the depth was then about ip fa- 

 thoms, and the proportion of the weight of the salt water to that of the same 

 quantity of fresh water, taken out of the river Thames, was as 42 to 41. 



One of the instruments was a glass-bottle, that held a quart of water, having 

 a brass ring fastened to its mouth, with a valve or flap, that opened inward, 

 so well fitted, that the bottle being filled more or less with water, none dropped 

 out, though forcibly shaken. This, let down 33 feet into the water with the 

 mouth downwards, and after a little stay drawn up, was found to be so very 

 near half full of water, at several trials, that it was thought fit to state the com- 

 pression of air at that depth to that measure, which at other depths was found 

 to hold the like proportions answerable to the depths. 



The quantity of the compression was known by weighing the bottle with the 

 water in it, after that a forcible depression of the flap had made way for the 

 eruption of the compressed air (which kept it up even when the bottle was 

 placed with the mouth upwards) and then filling the bottle full of the same 

 water, and weighing it again ; and lastly by weighing the bottle after the water 

 was all let out ; the weight of it being deducted, the first quantity of water 

 weighed just half as much as the second, or so near it that the fraction was 

 not considerable : Whence it was concluded, that the quantity of the air, that 

 filled the bottle before it was immersed in the water, was at the depth of 33 

 feet, compressed into half the space it took up before, and so proportionably at 

 other depths. 



This was confirmed by repeated experiments made with the other instru- 

 ment ; which was a cylinder of glass, about two feet long, close at one end, 

 and having the other end drawn out small by a lamp, and turned down a little 

 way, after the manner expressed in fig. 1. pi. 14. This cylinder was immersed 

 perpendicularly with the crooked end uppermost ; by which, as it sunk in the 

 water, the pressure gradually forced in so much water as thrust out the air pro- 

 portionable to every depth, till the cylinder was so far immersed, that the hole 

 of the crooked part of it was just 33 feet under water ; and then it being drawn 

 up, by measuring from the bottom of the cylinder to the height of the hole in 



