After the air-pump had been discovered, everybody set to work to try it in various ways. Boyle brought a small closed bladder into the globe and worked the pump. He found that the bladder at once expanded, and finally burst; evidently because the pressure of the air inside the bladder was no longer balanced by the pressure of the air in the globe. He also put a little cup of water under the air-pump, and found that it gave off bubbles and finally appeared to boil, although it was not hot. Boyle thought that water could be converted into air, but in this he was wrong, because we know now that steam is given off from water under low pressures of air even when the temperature is very low. Boyle found also that water falling in a vacuum makes the sound of some metallic object. Meanwhile, Guericke was also actively improving his apparatus, and soon he was able to pump out nearly all the air, and to leave only one-thirtieth of the original amount in the vessel he employed. He next succeeded in proving that a vacuum does not allow sound to pass through it. He placed a clock into the vacuum, and as he pumped the air out more and more, the striking of the clock was heard more and more faintly, until it became quite inaudible. He was so convinced of the powerful effect of the suction of an empty space, that he said that if a man were to blow his breath into a large vacuum, that breath would be his last. [Illustration: Fig. 39.--Guericke’s experiment to show the pressure upon the piston of a cylinder from which air was being extracted.] The Marshal of the Emperor refused to believe this, but Guericke undertook to convince him of the truth in another manner. He constructed a cylinder with a piston which moved in it air-tight. This piston was suspended by a rope over a pulley, and to the end of the rope twenty small ropes were attached, and each of these was held by a strong man. They pulled up the piston until it was at the top of the cylinder. Into the bottom of the cylinder a small hole was bored, and into this hole Guericke introduced the nozzle of his empty globe, which was stopped by means of a cock. On turning the cock, the air in the cylinder rushed into the empty globe, or rather it was driven in by the force of the outer air. So great was this force, that the twenty strong men holding the ropes were pulled violently forward and were quite unable to keep the piston up. A somewhat similar arrangement was used for firing shots without powder.