WEBVTT 00:00:06.762 --> 00:00:11.233 Aristotle famously said, "Nature fears of empty space" 00:00:11.233 --> 00:00:16.017 when he claimed that a true vacuum, a space devoid of matter, could not exist 00:00:16.017 --> 00:00:19.105 because the surrounding matter would immediately fill it. 00:00:19.105 --> 00:00:21.994 Fortunately, he turned out to be wrong. 00:00:21.994 --> 00:00:25.010 A vacuum is a key component of the barometer, 00:00:25.010 --> 00:00:27.492 an instrument for measuring air pressure. 00:00:27.492 --> 00:00:30.107 And because air pressure correlates to temperature 00:00:30.107 --> 00:00:32.032 and rapid shifts in it can contribute to 00:00:32.032 --> 00:00:35.643 hurricanes, tornadoes and other extreme weather events, 00:00:35.643 --> 00:00:38.156 a barometer is one of the most essential tools 00:00:38.156 --> 00:00:41.840 for weather forecasters and scientists alike. 00:00:41.840 --> 00:00:44.766 How does a barometer work, and how was it invented? 00:00:44.766 --> 00:00:46.448 Well, it took awhile. 00:00:46.448 --> 00:00:49.741 Because the theory of Aristotle and other ancient philosophers 00:00:49.741 --> 00:00:54.986 regarding the impossibility of a vacuum seemed to hold true in everyday life, 00:00:54.986 --> 00:00:59.040 few seriously thought to question it for nearly 2,000 years -- 00:00:59.040 --> 00:01:01.541 until necessity raised the issue. 00:01:01.541 --> 00:01:05.550 In the early 17th century, Italian miners faced a serious problem 00:01:05.550 --> 00:01:08.442 when they found that their pumps could not raise water 00:01:08.442 --> 00:01:10.822 more than 10.3 meters high. 00:01:10.822 --> 00:01:14.883 Some scientists at the time, including one Galileo Galilei, 00:01:14.883 --> 00:01:20.310 proposed that sucking air out of the pipe was what made water rise to replace the void. 00:01:20.310 --> 00:01:25.606 But that its force was limited and could lift no more than 10.3 meters of water. 00:01:25.606 --> 00:01:28.523 However, the idea of a vacuum existing at all 00:01:28.523 --> 00:01:30.728 was still considered controversial. 00:01:30.728 --> 00:01:33.647 And the excitement over Galileo's unorthodox theory, 00:01:33.647 --> 00:01:38.231 led Gasparo Berti to conduct a simple but brilliant experiment 00:01:38.231 --> 00:01:40.213 to demonstrate that it was possible. 00:01:40.213 --> 00:01:42.402 A long tube was filled with water 00:01:42.402 --> 00:01:46.321 and placed standing in a shallow pool with both ends plugged. 00:01:46.321 --> 00:01:48.948 The bottom end of the tube was then opened 00:01:48.948 --> 00:01:51.429 and water poured out into the basin 00:01:51.429 --> 00:01:56.096 until the level of the water remaining in the tube was 10.3 meters. 00:01:56.096 --> 00:02:00.017 With a gap remaining at the top, and no air having entered the tube, 00:02:00.017 --> 00:02:04.401 Berti had succeeded in directly creating a stable vacuum. 00:02:04.401 --> 00:02:08.497 But even though the possibility of a vacuum had been demonstrated, 00:02:08.497 --> 00:02:11.411 not everyone was satisfied with Galileo's idea 00:02:11.411 --> 00:02:14.463 that this empty void was exerting some mysterious 00:02:14.463 --> 00:02:16.943 yet finite force on the water. 00:02:16.943 --> 00:02:20.973 Evangelista Torricelli, Galileo's young pupil and friend, 00:02:20.973 --> 00:02:23.676 decided to look at the problem from a different angle. 00:02:23.676 --> 00:02:27.017 Instead of focusing on the empty space inside the tube, 00:02:27.017 --> 00:02:30.390 he asked himself, "What else could be influencing the water?" 00:02:30.390 --> 00:02:34.328 Because the only thing in contact with the water was the air surrounding the pool, 00:02:34.328 --> 00:02:38.159 he believed the pressure from this air could be the only thing preventing 00:02:38.159 --> 00:02:41.247 the water level in the tube from dropping further. 00:02:41.247 --> 00:02:45.151 He realized that the experiment was not only a tool to create a vacuum, 00:02:45.151 --> 00:02:47.288 but operated as a balance 00:02:47.288 --> 00:02:50.681 between the atmospheric pressure on the water outside the tube 00:02:50.681 --> 00:02:53.895 and the pressure from the water column inside the tube. 00:02:53.895 --> 00:02:58.534 The water level in the tube decreases until the two pressures are equal, 00:02:58.534 --> 00:03:02.342 which just happens to be when the water is at 10.3 meters. 00:03:02.342 --> 00:03:04.655 This idea was not easily accepted, 00:03:04.655 --> 00:03:07.553 as Galileo and others had traditionally thought 00:03:07.553 --> 00:03:12.064 that atmospheric air has no weight and exerts no pressure. 00:03:12.064 --> 00:03:14.898 Torricelli decided to repeat Berti's experiment 00:03:14.898 --> 00:03:16.851 with mercury instead of water. 00:03:16.851 --> 00:03:20.168 Because mercury was denser, it fell farther than the water 00:03:20.168 --> 00:03:23.994 and the mercury column stood only about 76 centimeters tall. 00:03:23.994 --> 00:03:28.245 Not only did this allow Torricelli to make the instrument much more compact, 00:03:28.245 --> 00:03:32.341 it supported his idea that weight was the deciding factor. 00:03:32.341 --> 00:03:37.891 A variation on the experiment used two tubes with one having a large bubble at the top. 00:03:37.891 --> 00:03:42.136 If Galileo's interpretation had been correct, the bigger vacuum in the second tube 00:03:42.136 --> 00:03:45.805 should have exerted more suction and lifted the mercury higher. 00:03:45.805 --> 00:03:48.840 But the level in both tubes was the same. 00:03:48.840 --> 00:03:53.085 The ultimate support for Torricelli's theory came via Blaise Pascal 00:03:53.085 --> 00:03:56.308 who had such a mercury tube taken up a mountain 00:03:56.308 --> 00:03:58.278 and showed that the mercury level dropped 00:03:58.278 --> 00:04:02.031 as the atmospheric pressure decreased with altitude. 00:04:02.031 --> 00:04:05.451 Mercury barometers based on Torricelli's original model 00:04:05.451 --> 00:04:10.366 remained one of the most common ways to measure atmospheric pressure until 2007 00:04:10.366 --> 00:04:13.623 when restrictions on the use of mercury due to its toxicity 00:04:13.623 --> 00:04:16.853 led to them no longer being produced in Europe. 00:04:16.853 --> 00:04:18.932 Nevertheless, Torricelli's invention, 00:04:18.932 --> 00:04:22.076 born of the willingness to question long accepted dogmas 00:04:22.076 --> 00:04:25.802 about vacuums and the weight of air, is an outstanding example 00:04:25.802 --> 00:04:29.077 of how thinking outside of the box -- or the tube -- 00:04:29.077 --> 00:04:30.589 can have a heavy impact.