He had taken a piece of strong glass tubing fully twelve feet in length. (The experiment was made by a well-lighted staircase, the tube being suspended by strings.) The glass was heated more than a foot from the lower end, and bent so that the shorter leg of twelve inches was parallel with the longer. The former was hermetically sealed at the top and marked off in forty-eight quarter-inch spaces. Into the opening of the longer leg, also graduated, mercury was poured. At first only enough was introduced to fill the arch, or bent part of the tube below the graduated legs. The tube was then inclined so that the air might pass from one leg to the other, and equality of pressure at the start be assured. Then more mercury was introduced and every time that the air in the shorter leg was compressed a half or a quarter of an inch, a record was made of the height of the mercury in the long leg of the tube. Boyle reasoned that the compressed air was sustaining the pressure of the column of mercury in the long leg _plus_ the pressure of the atmosphere at the tube's opening, equivalent to 29-2/16 inches of mercury. Some of the results were as follows: When the air in the short tube was compressed from 12 to 3 inches, it was under a pressure of 117-9/16 inches of mercury; when compressed to 4 it was under pressure of 87-15/16 inches of mercury; when compressed to 6, 58-13/16; to 9, 39-5/8. Of course, when at the beginning of the experiment there were 12 inches of air in the short tube, it was under the pressure of the atmosphere, equal to that of 29-2/16 inches of mercury. Boyle with characteristic caution was not inclined to draw too general a conclusion from his experiment. However, it was evident, making allowance for some slight irregularity in the experimental results, that air reduced under pressure to one half its original volume, doubles its resistance; and that if it is further reduced to one half,--for example, from six to three inches,--it has four times the resistance of common air. In fact, Boyle had sustained the hypothesis that supposes the pressures and expansions to be in reciprocal proportions. REFERENCES Sir Robert S. Ball, _Great Astronomers_. Robert Boyle, _Works_ (edited by Thomas Birch). Sir David Brewster, _Martyrs of Science_. J. L. E. Dreyer, _Tycho Brahe_. Sir Oliver Lodge, _Pioneers of Science_. Flora Masson, _Robert Boyle; a Biography_. CHAPTER VIII COÖPERATION IN SCIENCE--THE ROYAL SOCIETY The period from 1637 to 1687 affords a good illustration of the value for the progress of science of the coöperation in the pursuit of truth of men of different creeds, nationalities, vocations, and social ranks. At, or even before, the beginning of that period the need of coöperation was indicated by the activities of two men of pronouncedly social temperament and interests, namely, the French Minim father, Mersenne, and the Protestant Prussian merchant, Samuel Hartlib.