COMPRESSION, the act of pressing or squeezing some matter, so as to set its parts nearer to each other, and make it possess less space.
Water was, during a very long period, considered as a fluid perfectly unelastie that is, unyielding, or incompressible ; and this opinion was corroborated by an experiment of the Academy del Cimento in Italy. About a century and a half ago, the members of that academy endeavour ed to ascertain whether water was capa ble of being compressed in any degree. For this purpose they filled a hollow metallic sphere with that fluid, and stop ped the aperture very accurately. This ball then was pressed in a proper ma chine, but no contraction could be ob served; nor, indeed, was the apparatus capable of manifesting small degrees of compression. Hence they concluded that water was not capable of compression. This opinion prevailed until the year 1761, when the ingenious Mr. Canton discovered the compressibility of water, and of other liquids, which he immedi. ately made known to the Royal Society. He took a glass tube, having a ball at one end, filled the ball and part of the tube with water, which he had deprived air as much as it was in his power ; then placed the glass thus filled under the receiver of an air-pump ; and on ex hausting the receiver, which removed the pressure of the atmosphere from over the water and the glass vessel which contained it, in consequence of which the water rose a little way into the tube, viz. expanded itself. He then
placed the apparatus under the receiver of a condensing engine, and on forcing the air into it, which increased the pres sure upon the water, a diminution of bulk evidently took place; the water descend ing a little way within the tube. "In this manner," Mr. Canton says, " I have found by repeated trials, when the heat of the air has been about 50°, and the mercury at a mean height in the barome ter, that the water will expand and rise in the tube by removing the weight of the atmosphere, one part in 21740, and will be as much compressed under the weight of an additional atmosphere. Therefore the compression of water by twice the weight of the atmosphere is one part in 10870." "Water has the re markable property of being more com pressible in winter than in summer, which is contrary to what I have observ ed both in spirits of wine and oil of olives." By the same means, and in the same circumstances, Mr. Canton ascer tained the property of being compressed in some other fluids, and the results are as in the following table : Millionth part.
Compression of spirit of wine - 66 oil of olives - - - 48 . - - - - rain water - - - - 46 sea water 40 mercury 3