Page:Micrographia - or some physiological descriptions of minute bodies made by magnifying glasses with observations and inquiries thereupon.djvu/339

Rh in the box, till the surface of that within the Tube be equal to it, for the Quicksilver (as I have elsewhere prov'd) being more heterogeneous to the Glass then the Air, will not naturally rise up so high within the small Pipe, as the superficies of the Mercury in the box, and therefore you are to observe, how much below the outward superficies of the Mercury in the box, that of the same in the Tube does stand, when the top being open, free ingress is admitted to the outward Air.

Having thus done, I permitted the Cylinder, or small Pipe, to rise out of the box, till I found the surface of the Quicksilver in the Pipe to be two inches above that in the box, and found the Air to have expanded it self but one sixteenth part of an inch; then drawing up the small pipe, till I found the height of the Quicksilver within to be four inches above that without, I observed the Air to be expanded only of an inch more then it was at first, and to take up the room of 1  inch: then I raised the Tube till the Cylinder was six inches high, and found the Air to take up 1 inches of room in the Pipe; then to 8, 10, 12. &c. the expansion of the Air that I found to each of which Cylinders are set down in the following Table; where the first row signifies the height of the Mercurial Cylinder; the next, the expansion of the Air; the third, the pressure of the Atmosphere, or the highest Cylinder of Mercury, which was then neer thirty inches: The last signifies the force of the Air so expanded, which is found by substracting the first row of numbers out of the third; for having found, that the outward Air would then keep up the Quicksilver to thirty inches, look whatever of that height is wanting must be attributed to the Elater of the Air depressing. And therefore having the Expansion in the second row, and the height of the subjacent Cylinder of Mercury in the first, and the greatest height of the Cylinder of Mercury, which of it self counterballances the whole pressure of the Atmosphere; by substracting the numbers of the first row out of the numbers of the third, you will have the measure of the Cylinders so deprest, and consequently the force of the Air, in the several Expansions, registred.

Rh