The manner of proceeding therein was this: I took a Tube about five foot long, one of whose ends was sealed up, and bended in the form of a _Syphon_, much like that represented in the fourth Figure of the 37. _Scheme_, one side whereof AD, that was open at A, was about fifty inches long, the other side BC, shut at B, was not much above seven inches long, then placing it exactly perpendicular, I pour’d in a little Quicksilver, and found that the Air BC was 6⅞ inches, or very near to seven; then pouring in Quicksilver at the longer Tube, I continued filling of it till the Air in the shorter part of it was contracted into half the former dimensions, and found the height exactly nine and twenty inches; and by making several other tryals, in several other degrees of condensation of the Air, I found them exactly answer the former _Hypothesis_. But having (by reason it was a good while since I first made) forgotten many particulars, and being much unsatisfied in others, I made the Experiment over again, and, from the several tryals, collected the former part of the following Table: Where in the row next the left hand 24. signifies the dimensions of the Air, sustaining only the pressure of the _Atmosphere_, which at that time was equal to a _Cylinder_ of _Mercury_ of nine and twenty inches: The next Figure above it (20) was the dimensions of the Air induring the first compression, made by a _Cylinder_ of _Mercury_ 5³⁄₁₆ high, to which the pressure of the _Atmosphere_ nine and twenty inches being added, the elastick strength of the Air so comprest will be found 34³⁄₁₆, &c. _A Table of the Elastick power of the Air, both Experimentally and Hypothetically calculated, according to its various Dimensions._