1 00:00:06,762 --> 00:00:11,233 Aristotle famously said, "Nature fears of empty space" 2 00:00:11,233 --> 00:00:16,017 when he claimed that a true vacuum, a space devoid of matter, could not exist 3 00:00:16,017 --> 00:00:19,105 because the surrounding matter would immediately fill it. 4 00:00:19,105 --> 00:00:21,994 Fortunately, he turned out to be wrong. 5 00:00:21,994 --> 00:00:25,010 A vacuum is a key component of the barometer, 6 00:00:25,010 --> 00:00:27,492 an instrument for measuring air pressure. 7 00:00:27,492 --> 00:00:30,107 And because air pressure correlates to temperature 8 00:00:30,107 --> 00:00:32,032 and rapid shifts in it can contribute to 9 00:00:32,032 --> 00:00:35,643 hurricanes, tornadoes and other extreme weather events, 10 00:00:35,643 --> 00:00:38,156 a barometer is one of the most essential tools 11 00:00:38,156 --> 00:00:41,840 for weather forecasters and scientists alike. 12 00:00:41,840 --> 00:00:44,766 How does a barometer work, and how was it invented? 13 00:00:44,766 --> 00:00:46,448 Well, it took awhile. 14 00:00:46,448 --> 00:00:49,741 Because the theory of Aristotle and other ancient philosophers 15 00:00:49,741 --> 00:00:54,986 regarding the impossibility of a vacuum seemed to hold true in everyday life, 16 00:00:54,986 --> 00:00:59,040 few seriously thought to question it for nearly 2,000 years -- 17 00:00:59,040 --> 00:01:01,541 until necessity raised the issue. 18 00:01:01,541 --> 00:01:05,550 In the early 17th century, Italian miners faced a serious problem 19 00:01:05,550 --> 00:01:08,442 when they found that their pumps could not raise water 20 00:01:08,442 --> 00:01:10,822 more than 10.3 meters high. 21 00:01:10,822 --> 00:01:14,883 Some scientists at the time, including one Galileo Galilei, 22 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. 23 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. 24 00:01:25,606 --> 00:01:28,523 However, the idea of a vacuum existing at all 25 00:01:28,523 --> 00:01:30,728 was still considered controversial. 26 00:01:30,728 --> 00:01:33,647 And the excitement over Galileo's unorthodox theory, 27 00:01:33,647 --> 00:01:38,231 led Gasparo Berti to conduct a simple but brilliant experiment 28 00:01:38,231 --> 00:01:40,213 to demonstrate that it was possible. 29 00:01:40,213 --> 00:01:42,402 A long tube was filled with water 30 00:01:42,402 --> 00:01:46,321 and placed standing in a shallow pool with both ends plugged. 31 00:01:46,321 --> 00:01:48,948 The bottom end of the tube was then opened 32 00:01:48,948 --> 00:01:51,429 and water poured out into the basin 33 00:01:51,429 --> 00:01:56,096 until the level of the water remaining in the tube was 10.3 meters. 34 00:01:56,096 --> 00:02:00,017 With a gap remaining at the top, and no air having entered the tube, 35 00:02:00,017 --> 00:02:04,401 Berti had succeeded in directly creating a stable vacuum. 36 00:02:04,401 --> 00:02:08,497 But even though the possibility of a vacuum had been demonstrated, 37 00:02:08,497 --> 00:02:11,411 not everyone was satisfied with Galileo's idea 38 00:02:11,411 --> 00:02:14,463 that this empty void was exerting some mysterious 39 00:02:14,463 --> 00:02:16,943 yet finite force on the water. 40 00:02:16,943 --> 00:02:20,973 Evangelista Torricelli, Galileo's young pupil and friend, 41 00:02:20,973 --> 00:02:23,676 decided to look at the problem from a different angle. 42 00:02:23,676 --> 00:02:27,017 Instead of focusing on the empty space inside the tube, 43 00:02:27,017 --> 00:02:30,390 he asked himself, "What else could be influencing the water?" 44 00:02:30,390 --> 00:02:34,328 Because the only thing in contact with the water was the air surrounding the pool, 45 00:02:34,328 --> 00:02:38,159 he believed the pressure from this air could be the only thing preventing 46 00:02:38,159 --> 00:02:41,247 the water level in the tube from dropping further. 47 00:02:41,247 --> 00:02:45,151 He realized that the experiment was not only a tool to create a vacuum, 48 00:02:45,151 --> 00:02:47,288 but operated as a balance 49 00:02:47,288 --> 00:02:50,681 between the atmospheric pressure on the water outside the tube 50 00:02:50,681 --> 00:02:53,895 and the pressure from the water column inside the tube. 51 00:02:53,895 --> 00:02:58,534 The water level in the tube decreases until the two pressures are equal, 52 00:02:58,534 --> 00:03:02,342 which just happens to be when the water is at 10.3 meters. 53 00:03:02,342 --> 00:03:04,655 This idea was not easily accepted, 54 00:03:04,655 --> 00:03:07,553 as Galileo and others had traditionally thought 55 00:03:07,553 --> 00:03:12,064 that atmospheric air has no weight and exerts no pressure. 56 00:03:12,064 --> 00:03:14,898 Torricelli decided to repeat Berti's experiment 57 00:03:14,898 --> 00:03:16,851 with mercury instead of water. 58 00:03:16,851 --> 00:03:20,168 Because mercury was denser, it fell farther than the water 59 00:03:20,168 --> 00:03:23,994 and the mercury column stood only about 76 centimeters tall. 60 00:03:23,994 --> 00:03:28,245 Not only did this allow Torricelli to make the instrument much more compact, 61 00:03:28,245 --> 00:03:32,341 it supported his idea that weight was the deciding factor. 62 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. 63 00:03:37,891 --> 00:03:42,136 If Galileo's interpretation had been correct, the bigger vacuum in the second tube 64 00:03:42,136 --> 00:03:45,805 should have exerted more suction and lifted the mercury higher. 65 00:03:45,805 --> 00:03:48,840 But the level in both tubes was the same. 66 00:03:48,840 --> 00:03:53,085 The ultimate support for Torricelli's theory came via Blaise Pascal 67 00:03:53,085 --> 00:03:56,308 who had such a mercury tube taken up a mountain 68 00:03:56,308 --> 00:03:58,278 and showed that the mercury level dropped 69 00:03:58,278 --> 00:04:02,031 as the atmospheric pressure decreased with altitude. 70 00:04:02,031 --> 00:04:05,451 Mercury barometers based on Torricelli's original model 71 00:04:05,451 --> 00:04:10,366 remained one of the most common ways to measure atmospheric pressure until 2007 72 00:04:10,366 --> 00:04:13,623 when restrictions on the use of mercury due to its toxicity 73 00:04:13,623 --> 00:04:16,853 led to them no longer being produced in Europe. 74 00:04:16,853 --> 00:04:18,932 Nevertheless, Torricelli's invention, 75 00:04:18,932 --> 00:04:22,076 born of the willingness to question long accepted dogmas 76 00:04:22,076 --> 00:04:25,802 about vacuums and the weight of air, is an outstanding example 77 00:04:25,802 --> 00:04:29,077 of how thinking outside of the box -- or the tube -- 78 00:04:29,077 --> 00:04:30,589 can have a heavy impact.