0:00:06.762,0:00:11.233 Aristotle famously said,[br]"Nature fears of empty space" 0:00:11.233,0:00:16.017 when he claimed that a true vacuum, [br]a space devoid of matter, could not exist 0:00:16.017,0:00:19.105 because the surrounding matter[br]would immediately fill it. 0:00:19.105,0:00:21.994 Fortunately, he turned out to be wrong. 0:00:21.994,0:00:25.010 A vacuum is a key component[br]of the barometer, 0:00:25.010,0:00:27.492 an instrument for measuring air pressure. 0:00:27.492,0:00:30.107 And because air pressure [br]correlates to temperature 0:00:30.107,0:00:32.032 and rapid shifts in it can contribute to 0:00:32.032,0:00:35.643 hurricanes, tornadoes [br]and other extreme weather events, 0:00:35.643,0:00:38.156 a barometer is one of the[br]most essential tools [br] 0:00:38.156,0:00:41.840 for weather forecasters and scientists alike. 0:00:41.840,0:00:44.766 How does a barometer work,[br]and how was it invented? 0:00:44.766,0:00:46.448 Well, it took awhile. 0:00:46.448,0:00:49.741 Because the theory of Aristotle [br]and other ancient philosophers 0:00:49.741,0:00:54.986 regarding the impossibility of a vacuum[br]seemed to hold true in everyday life, 0:00:54.986,0:00:59.040 few seriously thought to question it[br]for nearly 2,000 years -- 0:00:59.040,0:01:01.541 until necessity raised the issue. 0:01:01.541,0:01:05.550 In the early 17th century,[br]Italian miners faced a serious problem 0:01:05.550,0:01:08.442 when they found that their pumps[br]could not raise water [br] 0:01:08.442,0:01:10.822 more than 10.3 meters high. 0:01:10.822,0:01:14.883 Some scientists at the time,[br]including one Galileo Galilei, 0:01:14.883,0:01:20.310 proposed that sucking air out of the pipe[br]was what made water rise to replace the void. 0:01:20.310,0:01:25.606 But that its force was limited and could lift[br]no more than 10.3 meters of water. 0:01:25.606,0:01:28.523 However, the idea of a [br]vacuum existing at all 0:01:28.523,0:01:30.728 was still considered controversial. 0:01:30.728,0:01:33.647 And the excitement over [br]Galileo's unorthodox theory, 0:01:33.647,0:01:38.231 led Gasparo Berti to conduct a simple[br]but brilliant experiment 0:01:38.231,0:01:40.213 to demonstrate that it was possible. 0:01:40.213,0:01:42.402 A long tube was filled with water[br] 0:01:42.402,0:01:46.321 and placed standing in a shallow pool [br]with both ends plugged. 0:01:46.321,0:01:48.948 The bottom end of the tube [br]was then opened 0:01:48.948,0:01:51.429 and water poured out into the basin 0:01:51.429,0:01:56.096 until the level of the water remaining [br]in the tube was 10.3 meters. 0:01:56.096,0:02:00.017 With a gap remaining at the top,[br]and no air having entered the tube, 0:02:00.017,0:02:04.401 Berti had succeeded in[br]directly creating a stable vacuum. 0:02:04.401,0:02:08.497 But even though the possibility [br]of a vacuum had been demonstrated, 0:02:08.497,0:02:11.411 not everyone was satisfied [br]with Galileo's idea 0:02:11.411,0:02:14.463 that this empty void [br]was exerting some mysterious 0:02:14.463,0:02:16.943 yet finite force on the water. 0:02:16.943,0:02:20.973 Evangelista Torricelli, [br]Galileo's young pupil and friend,[br] 0:02:20.973,0:02:23.676 decided to look at the problem[br]from a different angle. 0:02:23.676,0:02:27.017 Instead of focusing on the [br]empty space inside the tube, 0:02:27.017,0:02:30.390 he asked himself,[br]"What else could be influencing the water?" 0:02:30.390,0:02:34.328 Because the only thing in contact [br]with the water was the air surrounding the pool, 0:02:34.328,0:02:38.159 he believed the pressure from this air[br]could be the only thing preventing 0:02:38.159,0:02:41.247 the water level in the tube[br]from dropping further. 0:02:41.247,0:02:45.151 He realized that the experiment [br]was not only a tool to create a vacuum, 0:02:45.151,0:02:47.288 but operated as a balance 0:02:47.288,0:02:50.681 between the atmospheric pressure[br]on the water outside the tube 0:02:50.681,0:02:53.895 and the pressure from the[br]water column inside the tube. 0:02:53.895,0:02:58.534 The water level in the tube decreases[br]until the two pressures are equal, 0:02:58.534,0:03:02.342 which just happens to be[br]when the water is at 10.3 meters. 0:03:02.342,0:03:04.655 This idea was not easily accepted, 0:03:04.655,0:03:07.553 as Galileo and others [br]had traditionally thought 0:03:07.553,0:03:12.064 that atmospheric air has no weight[br]and exerts no pressure. 0:03:12.064,0:03:14.898 Torricelli decided to [br]repeat Berti's experiment[br] 0:03:14.898,0:03:16.851 with mercury instead of water. 0:03:16.851,0:03:20.168 Because mercury was denser, [br]it fell farther than the water 0:03:20.168,0:03:23.994 and the mercury column stood[br]only about 76 centimeters tall. 0:03:23.994,0:03:28.245 Not only did this allow Torricelli to make[br]the instrument much more compact, 0:03:28.245,0:03:32.341 it supported his idea that weight[br]was the deciding factor. 0:03:32.341,0:03:37.891 A variation on the experiment used two tubes[br]with one having a large bubble at the top. 0:03:37.891,0:03:42.136 If Galileo's interpretation had been correct,[br]the bigger vacuum in the second tube 0:03:42.136,0:03:45.805 should have exerted more suction[br]and lifted the mercury higher. 0:03:45.805,0:03:48.840 But the level in both tubes was the same. 0:03:48.840,0:03:53.085 The ultimate support for Torricelli's theory[br]came via Blaise Pascal 0:03:53.085,0:03:56.308 who had such a mercury tube[br]taken up a mountain 0:03:56.308,0:03:58.278 and showed that the mercury level dropped 0:03:58.278,0:04:02.031 as the atmospheric pressure[br]decreased with altitude. 0:04:02.031,0:04:05.451 Mercury barometers based on [br]Torricelli's original model 0:04:05.451,0:04:10.366 remained one of the most common ways[br]to measure atmospheric pressure until 2007 0:04:10.366,0:04:13.623 when restrictions on the use of[br]mercury due to its toxicity 0:04:13.623,0:04:16.853 led to them no longer[br]being produced in Europe. 0:04:16.853,0:04:18.932 Nevertheless, Torricelli's invention,[br] 0:04:18.932,0:04:22.076 born of the willingness to question[br]long accepted dogmas 0:04:22.076,0:04:25.802 about vacuums and the weight of air,[br]is an outstanding example 0:04:25.802,0:04:29.077 of how thinking outside of the box[br]-- or the tube -- 0:04:29.077,0:04:30.589 can have a heavy impact.