An Ocean of Air Read Online Free PDF Page A

had Otto von Guericke. With the machine that Hooke designed, Boyle would soon be able to make air come and go at will.
    While Hooke labored, the outside world grew increasingly fearful. The stability that Oliver Cromwell had brought to England was beginning to fray. Even nature seemed to be against him. The winter of 1657-58 was the severest on record, and bitter temperatures lasted until June. There were days of public fasting to try to ward off the evil that had befallen the country. On August 21, Cromwell fell ill, and the nation held its breath. Ten days later, England was blasted by a storm so violent that Cromwell's followers declared it was a warning of divine retribution against his detractors, and his enemies said the devil was riding in on the wind to claim the soul of the great traitor and king-slayer. Whatever the true reason for the storm, Cromwell had only a few more days to live, and his death heralded a new period of disarray.
    The Royalists began to agitate for the return of the king, while the Roundheads marshaled their forces under the banner of Cromwell's regrettably feeble son. Yet through all this, Boyle and Hooke remained oblivious. Safely ensconced in Oxford, they worked steadily on their air pump.
    It wasn't easy. Boyle was struggling desperately with distemper in his eyes. A few years earlier he had fallen off his horse in Ireland and contracted a protracted and debilitating illness. Soon afterward his sight had begun to trouble him, and there were times when he could scarcely make out the apparatus for himself. But still he was eager for what he called "the principal fruit I promised myself from our Engine." For Boyle already believed that Torricelli and von Guericke were right, that the driving force in Torricelli's quicksilver experiment was the weight of the air. And he also believed that with his new air pump, he would be able to convince the rest of the world.
    Boyle's idea was to take Torricelli's experiment and put the whole thing inside a vacuum. This had already been tried a couple of times, but without an air pump it had been very messy, involving attempts to fit one glass tube filled with quicksilver inside the vacuum created at the top of another. Hooke's adaptation of Otto von Guericke's invention was going to make the experiment much easier.
    At last, the pump was ready. Hooke's design consisted of a large glass globe, with a wide opening at the neck, which could hold about fifty pints. This would be the "receiver" of the pump, where the experiments were to take place. Attached below this was a hollow brass cylinder just over a foot long, into which a plunger covered with tanned leather was tightly rammed. Through a clever system of valves, both globe and cylinder could be opened to the outside air or sealed from it. Simply pulling the plunger downwards drew air out of the globe. Adjust the appropriate valves, repeat this process several times, and you have yourself a vacuum.
    The first step was to recreate Torricelli's experiment. Boyle and Hooke took a slender cylinder of glass about three feet long, closed at one end, and filled it with quicksilver. Then, as usual, they tipped it upside down into a box half filled with mercury. Just as expected, the mercury inside the tube began to fall until it reached a height of 29½ inches.
    The next part was more delicate. Box, tube, and all were attached to strings and let gently down to dangle in the middle of the glass globe. (The top of the glass tube still poked up through the neck of the receiver,
but Boyle slipped a tight cover over it to prevent any leaks.) As far as the mercury in the glass tube was concerned, nothing had changed. It still rested 29½ inches above the mercury in the box below.
    Now to begin sucking air out of the glass receiver. If Galileo was right, this should change nothing. According to him, the only force holding the quicksilver up was the sucking power of the vacuum in the closed space at the top of the glass