An Ocean of Air Read Online Free PDF Page B

Boyle was fluent in Latin, as in many other languages, he was unusual for philosophers of the time in that he chose to write in everyday, accessible English. Still more unusually, he eschewed the "normal" way of writing up science—philosophical discourses among fictitious persons—in favor of a straightforward description of his apparatus, what he did for each experiment, and the results he obtained. He wanted people to understand exactly what he had done, and even to be able to repeat it. In this sense, he was one of the world's first true scientists.
    The book was an immediate hit, not least because it contained much more than the proof of the pressing power of air. Boyle would never have been satisfied with merely confirming what Torricelli had already discovered. Armed with his new air pump, he had always wanted to go much farther.
    One of the first new things that Boyle discovered was that, unlike water, air seemed to have bounce. He'd noticed this almost as soon as he tried removing air from inside the glass globe. If you first pulled down the plunger to make a vacuum inside the brass cylinder, and only then opened the valve to the glass globe, air immediately whooshed from the globe into the cyclinder. Everyone in the room could hear it. If you closed off the valve, emptied the cylinder, and repeated the process, the whooshing still happened, but it was a bit less dramatic, with less air rushing out of the globe. And the next time you tried, even less air whooshed out.
    Boyle deduced that air must contain some kind of particles that squeeze against each other. When the globe was full of air it was like an overcrowded room; as soon as the valve was opened, particles spilled out. But with each drag of the pump, the remaining particles could spread out—and were hence much more reluctant to leave.
    Boyle didn't understand this quite as we do today—he imagined air to be something like a springy pile of flocks of wool. We now know that a piece of air the size of a sugar lump contains around 25 billion billion molecules all constantly darting about faster than the speed of sound. Every molecule crashes into another five billion times a second, and it is this incessant pinball barging that gives air its spring. It's why the billions of bouncing molecules inside a tire can hold up a truck, and why the weight of air doesn't only press downward but acts in every direction.
    Boyle wanted to find out what role, if any, this springy air plays in the perception of sound. Nobody really knew how sound moves around, although there was a vague notion that it had something to do with the atmosphere.
    He decided to try a careful experiment. Into his great glass globe he gently lowered a ticking watch, suspended from a thread. The watch was one of the latest models, which had a hand to mark out the seconds as well as the more usual minutes and hours. Using this, the experimenters would be able to assure themselves that the watch was still working as it dangled inside the globe.
    At first, the sound of ticking was clear even a foot away from the globe. But when the pump began removing air, something changed: The ticking grew fainter and fainter. At last, when the pump had removed as much air as possible, Boyle and his helpers pressed their ears to the side of the globe. They could see the newfangled second hand as it continued to work its way around the watch face. But though everyone in the room strained to pick up the slightest hint of ticking, nobody could hear a thing. The air that left the globe had taken with it the power to transmit sound.
    We now know that sound is made from vibrations. It can be transmitted through anything that wobbles—if your ear is touching something that's vibrating, you have no need of the air in between. But most of the sounds we care about happen at a distance, and for that our atmosphere is essential. Anything on Earth that makes a noise sets the air around it quivering, and our entire thick