The treatise on "The Spring of the Air" met with much opposition, and Boyle considered it necessary to defend his doctrine against the objections of Franciscus Linus and Hobbes. In this defence he described the experiment in connection with which he is most generally remembered. Linus had admitted that the air might possess a certain small amount of elasticity, but maintained that the force with which mercury rose in a barometer tube was due mainly to a totally different action, as though a string were pulling upon it from above. This was his funicular hypothesis. Boyle undertook to show that the pressure of the air might be made to support a much higher column of mercury than that of the barometer. To this end he took a glass tube several feet in length, and bent so as to form two vertical legs connected below. The shorter leg was little more than a foot long, and hermetically closed at the top. The longer leg was nearly eight feet in length, and open at the top. The tube was suspended by strings upon the staircase, the bend at the bottom pressing lightly against the bottom of a box placed to receive the mercury employed in case of accident. Each leg of the tube was provided with a paper scale. Mercury was poured in at the open end, the tube being tilted so as to allow some of the air to escape from the shorter limb until the mercury stood at the same level in both legs when the tube was vertical. The length of the closed tube occupied by the air was then just twelve inches. The height of the barometer was about 29-1/8 inches. Mercury was gently poured into the open limb by one operator, while another watched its height in the closed limb. The results of the experiments are given in the table on the opposite page. In this table the third column gives the result of adding to the second column the height of the barometer, which expresses in inches of mercury the pressure of the air on the free surface of the mercury in the longer limb. The fourth column gives the total pressure, in inches of mercury, on the hypothesis that the pressure of the air varies inversely as the volume. The agreement between the third and fourth columns is very close, considering the roughness of the experiment and that no trouble appears to have been taken to _calibrate_ the shorter limb of the tube, and justified Boyle in concluding that the hypothesis referred to expresses the relation between the volume and pressure of a given mass of air.