Volledige transcriptie van The Einstein Lens and a Tale of Two Eclipses

actually went around blind. 49 00:05:54,480 --> 00:06:01,620 They had no periscope. They simply just went underwater, went a certain distance, hoping for the best, the particular direction. 50 00:06:03,360 --> 00:06:11,760 But then Grupp invented the periscope in particular for a submarine, and that was extremely challenging business at the time to do that. 51 00:06:12,930 --> 00:06:24,300 Anyway, at one point in his his firm, which is in a place called Rat Mines in Dublin, it had 400 people working on optics. 52 00:06:24,930 --> 00:06:28,530 Here's an actual picture of his firm in rat minds. 53 00:06:29,130 --> 00:06:34,380 This is with the opening of the new building. And you note the clear. 54 00:06:36,400 --> 00:06:41,410 Health and safety. Cognisance, right? 55 00:06:41,530 --> 00:06:49,170 Yes. And. Here's one of his famous telescopes, the great Melbourne Telescope. 56 00:06:49,200 --> 00:06:53,910 So Melbourne, after the Gold Rush, had a lot of money. 57 00:06:53,940 --> 00:07:02,940 This is back in sort of 1840 748, and they decided they were going to do the local government decided on a prestige 58 00:07:03,150 --> 00:07:07,590 project which was to build the largest telescope in the Southern Hemisphere. 59 00:07:08,940 --> 00:07:13,530 They had virtually no astronomers, by the way, but they decided to build the telescope anyway. 60 00:07:16,950 --> 00:07:20,820 So Hargrove was commissioned it making the telescope. 61 00:07:21,120 --> 00:07:24,120 And that was actually the last one. 62 00:07:25,020 --> 00:07:32,400 Major telescope using Speculum Mirror. So you built using glass mirror after that, people started using glass and parks, etcetera. 63 00:07:33,570 --> 00:07:38,850 And but that telescope, actually, there had been a number of reincarnations of that telescope. 64 00:07:39,090 --> 00:07:46,630 And it was used up to about, I think about 15 years ago for the Metro Project, you know, 65 00:07:46,680 --> 00:07:54,120 for searching for massive objects in the halo of our galaxy, which were causing gravitational deflection. 66 00:07:55,250 --> 00:08:02,240 Gravitational lensing. So and then of course, there was the fire of Mount Stromlo and that telescope was destroyed. 67 00:08:02,480 --> 00:08:07,970 But in fact, the Museum of Victoria is now in the process of restoring it. 68 00:08:09,660 --> 00:08:19,890 Here's another one of his telescopes. This is the the largest refractor on mainland in Europe and Vienna. 69 00:08:19,920 --> 00:08:29,040 And this was built also by Howard Grubb. And he built sort of half of the telescopes for the car to see. 70 00:08:29,130 --> 00:08:32,650 The car to see was, in fact, the first survey. 71 00:08:32,670 --> 00:08:35,940 I mean, we were talking about surveys last night, astronomical surveys. 72 00:08:36,420 --> 00:08:46,840 And so this the car to see you from around the 1890s and it ran for quite a number of years was actually the first survey of the sky. 73 00:08:46,860 -->

00:08:55,650 Obviously, it was a photographic survey and it involved a number of universities and observatories around the world, 74 00:08:56,040 --> 00:09:02,340 including the Vatican Observatory. So that's why over here you see a group of nuns. 75 00:09:03,270 --> 00:09:09,930 So back in 1895, 1900, they were actually doing the measurements on on plates. 76 00:09:10,170 --> 00:09:17,490 Now, take that into consideration during your next survey and this telescope, 77 00:09:17,700 --> 00:09:21,269 which maybe some of you might know because it was an Oxford at one point, 78 00:09:21,270 --> 00:09:27,450 the Ratcliff telescope, some grubby construct that had ended up, of course, in Pretoria. 79 00:09:28,080 --> 00:09:35,280 But it was initially in Oxford, and this was constructed by Hart Group. 80 00:09:36,510 --> 00:09:41,940 Anyway, so let's start with the dust to give you some background about Hargrove himself. 81 00:09:42,390 --> 00:09:48,480 But he was very not only an instrument maker, but he was very interested in astronomy itself. 82 00:09:49,380 --> 00:09:57,630 Back in the 1900s, he organised an expedition to Spain to observe the kips there. 83 00:09:57,960 --> 00:10:05,820 And this was an expedition that involved the Royal Irish Academy and the Royal Dublin Society. 84 00:10:06,390 --> 00:10:13,170 So they they they duly headed off to Spain, initially was told an enormous number of people were going to go. 85 00:10:13,180 --> 00:10:21,600 But then just around that period, there was problems with the Boer War, etc. and the net result of that was not so many people wanted to travel. 86 00:10:24,060 --> 00:10:31,290 So anyway, they headed off to Spain. As you can see here, you have a 10th of a point. 87 00:10:31,640 --> 00:10:35,190 Oh, there is one. I have one just here for. 88 00:10:42,230 --> 00:10:46,820 I've got one. Steve Yeah, no problem, sir. You should have taken this out right at the beginning. 89 00:10:49,370 --> 00:10:52,700 Yeah. So that's decided to die. 90 00:10:56,140 --> 00:11:00,260 This one. Oh, this one? 91 00:11:00,280 --> 00:11:09,030 Yeah. Okay, so let's see. Okay. 92 00:11:09,090 --> 00:11:22,140 So it works very well. Alright. So here is actually the group in the senior in in in Spain, the travelled there for the 1900s of clips. 93 00:11:22,980 --> 00:11:25,020 This is actually Hargrove himself. 94 00:11:25,380 --> 00:11:32,400 This is a guy called Charles Jasper Jolly who was director of Dun Cinque Observatory, which is actually part of my own institute. 95 00:11:32,400 --> 00:11:36,360 Now, this guy is his name is Wilson. 96 00:11:36,360 --> 00:11:39,480 He did a lot of work on the sun and some of you may have heard of Wilson. 97 00:11:40,410 --> 00:11:48,150 He was also made the first temperature measurement of the sun, and he came from a place near Dublin. 98 00:11:48,630 --> 00:11:53,160 And what I thought was very interesting about this picture is that clearly Wilson, 99 00:11:53,160

--> 00:11:59,280 W.E. Wilson thought, you know, he was going off to Spain and he would require his helmet. 100 00:11:59,610 --> 00:12:04,830 All right. The deepest, darkest Spain. So whereas this is Rupert. 101 00:12:05,670 --> 00:12:09,150 This is Rupert Grove, the son of Howard Grove. 102 00:12:09,390 --> 00:12:16,320 And he has the more the modern idea of what going to Spain involves, but with the sort of straw hat, etc. 103 00:12:16,320 --> 00:12:26,520 So you can see the cultural transition of the current man. So here you see them setting up the equipment for the 1900s eclipse. 104 00:12:26,520 --> 00:12:34,320 You can see Wilson there in the background. And but this is the particular instrument that I want to draw your attention to. 105 00:12:34,530 --> 00:12:41,280 So this is Jolie with the 24th photographic camera. 106 00:12:41,310 --> 00:12:47,760 So here you see where the photographic plate would have gone. And you can just about see it peering over the edge here. 107 00:12:47,980 --> 00:12:51,450 There was a see the start, which, of course, just takes the light from the sun. 108 00:12:52,230 --> 00:12:58,980 It turns as the sun moves, essentially. Or is half of the race because of the law of law of reflection. 109 00:12:59,280 --> 00:13:05,130 And so it then sends the light into this stationary tube, which has a lens at the front. 110 00:13:05,580 --> 00:13:17,819 And the image is produced back here. So, of course, what they were trying to do was image the corona of the sun and which they duly did. 111 00:13:17,820 --> 00:13:26,040 It was extremely, very good conditions. And this is actually an image from the 1900s eclipse, 112 00:13:26,040 --> 00:13:31,440 which is actually in the raw in our academy that use this for an inch lens, which was 20 foot focal length. 113 00:13:31,920 --> 00:13:36,000 And you can see here a number of prominences coming out of the sun. 114 00:13:36,990 --> 00:13:42,660 Now, this picture, by the way, several people have asked me, wow, I didn't realise they had colour photography in 1900. 115 00:13:42,780 --> 00:13:46,230 They didn't. These this was coloured afterwards. Right. 116 00:13:47,100 --> 00:13:54,060 So just in case you're wondering that. But nevertheless, I think for 1900, you can see there is, you know, a very good quality. 117 00:13:56,200 --> 00:14:05,110 Actually what I did at one point. I mean, as I said, this this particular eclipse well, eclipse is normally visible over a very long track. 118 00:14:05,380 --> 00:14:19,510 And in this case, it was visible all the way from the US through places like Georgia, South Georgia, North Carolina to Spain, Portugal, Spain, etc. 119 00:14:19,960 --> 00:14:28,180 So there are quite a few records of this eclipse and here you see a little sort of prominences here. 120 00:14:28,360 --> 00:14:37,060 They're the same, more or less the same ones there in Spain. This is a couple of hours difference because it took time for the for the solar

for 121 00:14:37,240 --> 00:14:42,430 for the track of the eclipse to move across the Atlantic from the US over to Europe. 122 00:14:42,910 --> 00:14:48,270 But you can see here that this is actually from the Smithsonian Archive. 123 00:14:48,280 --> 00:14:59,260 They had a station at North Carolina and a guy called Thomas Smiley, who is the photographer for the Smithsonian, 124 00:14:59,620 --> 00:15:07,900 actually recorded what's probably the first photograph of you recorded CME because you can see suddenly this, 125 00:15:08,440 --> 00:15:14,470 you know, the foot points here have developed into a major problems here, which has been injected into the corona. 126 00:15:16,240 --> 00:15:23,200 So we then kind of fast forwards a number of years. 127 00:15:25,880 --> 00:15:31,700 And as you know, and as Steve has already mentioned, towards the end of 1915, 128 00:15:32,510 --> 00:15:39,500 Einstein came up with this prediction that for the deflection of starlight when an eclipse occurs. 129 00:15:39,980 --> 00:15:46,280 And he predicted basically that, as you can see from here, the light of the of a star, 130 00:15:46,280 --> 00:15:52,729 which, of course, passes close to the sun, is bent, is altered in such a fashion. 131 00:15:52,730 --> 00:16:01,080 As you can see, I think from this diagram, the stars appear to move away from the sun itself compared to their normal position. 132 00:16:01,100 --> 00:16:06,560 So in the absence of the sun, and this is purely an effect of gravitational deflection. 133 00:16:08,720 --> 00:16:16,879 And he predicted the maximum amount will be 1.75 arcseconds and it scales with distance away from the sun so 134 00:16:16,880 --> 00:16:23,450 that to be the value would get for a star just at the surface of the sun or appearing to be at the surface. 135 00:16:23,690 --> 00:16:27,470 And of course, if you go to twice as far away, it's only half of that value. 136 00:16:29,270 --> 00:16:32,570 So that was the prediction in 1915. 137 00:16:32,720 --> 00:16:40,010 Now testing that prediction, there was there was a problem in trying to test the prediction, which is, of course, the First World War. 138 00:16:41,310 --> 00:16:46,230 And so it wasn't feasible to mount an eclipse expedition. 139 00:16:46,860 --> 00:16:55,329 So but back in 1917 then there was a this is a great title. 140 00:16:55,330 --> 00:17:04,080 So the Royal Astronomical Society and the Royal Society came together to form what was called a joint permanent eclipse committee. 141 00:17:05,400 --> 00:17:11,850 No, I still don't understand that title. No clips is permanent and hopefully no committee is permanent. 142 00:17:12,150 --> 00:17:19,260 So although I have my doubts in some cases, but anyway, they came together. 143 00:17:19,260 --> 00:17:23,790 They came up with this idea of an expedition, but they had a basic problem. 144 00:17:24,240 --> 00:17:29,190 And the basic problem was this that most of the Royal Society's Instrumentation and Royal 145 00:17:29,190 --> 00:17:35,700 Astronomical Society's instrumentation had been sent off to an eclipse in Russia in 1914. 146 00:17:36,180 --> 00:17:43,140 And then what happened was, of course, the First World War broke out, so they didn't get the equipment back. 147 00:17:43,230 --> 00:17:48,690 The astronomers got back, but the equipment was held up, of course, at the end of the war. 148 00:17:48,690 --> 00:17:52,139 Then you had the Bolshevik Revolution and they still didn't get their equipment back. 149 00:17:52,140 --> 00:17:55,800 In fact, they didn't get it back until the ninth, I think around 1925. 150 00:17:57,510 --> 00:18:07,290 So they were stuck and they asked to the Royal Irish Academy if they could assist by 151 00:18:07,290 --> 00:18:13,320 giving them some equipment from the Royal Irish Academy jus for previous eclipses. 152 00:18:14,580 --> 00:18:20,650 So there was actually a particular priest whose name was Courtney. 153 00:18:20,670 --> 00:18:25,830 Courtney. He was a stoney horse, which is in northern England, the school there. 154 00:18:25,950 --> 00:18:31,860 But he had associations with the Royal Academy and realised the potential of the equipment that had already been there. 155 00:18:32,100 --> 00:18:36,420 So they asked the Rowan Irish Academy for this equipment and that was duly of course a loan to them. 156 00:18:38,040 --> 00:18:46,170 So the idea behind the Eclipse expeditions was that there were actually two expeditions because chances were that maybe one of the, 157 00:18:47,230 --> 00:19:01,350 you know, might be cloudy. So the two sites that were chosen were kept off the west coast of Africa, but also a place called Sobral in Brazil. 158 00:19:02,190 --> 00:19:05,519 So those are the two sites and they're in the diagram. 159 00:19:05,520 --> 00:19:08,490 You can actually see the track of the eclipse itself. 160 00:19:11,660 --> 00:19:17,750 And it was regarded as an extremely favourable eclipse for measuring the deflection of starlight. 161 00:19:17,780 --> 00:19:25,010 Why? Because the sun was actually in a cluster behind each cluster, as you can see up here. 162 00:19:25,580 --> 00:19:31,990 We have used this one. You have. 163 00:19:32,000 --> 00:19:35,329 This is the tourist bowl. This is Aldebaran. 164 00:19:35,330 --> 00:19:42,710 This to be here. And this is the Hyades all all these stars here and up here at Hyades cluster. 165 00:19:42,920 --> 00:19:51,230 So there was a lot of stars. The sun was in a sort of perfect position because you could use a lot of these stars for reference purposes. 166 00:19:51,530 --> 00:19:58,430 And in particular, what I just want to point out is this star capital, which was the it's a double. 167 00:20:00,290 --> 00:20:10,730 It's a real double. It's not just an optical double. And capital was, you know, essentially the nearest star to the sun or nearest double star. 168 00:20:11,870 --> 00:20:20,870 So the idea was to

use the sun, other stars in the hyades to make measurements of the gravitational deflection of stars. 169 00:20:21,710 --> 00:20:27,230 Normally, the sun isn't in such a such a good position from the point of view of getting bright stars. 170 00:20:27,770 --> 00:20:38,110 So the eclipse. The Eclipse parties went out at two sets of instrumentation, by the way, and that actually involved Oxford as well. 171 00:20:38,120 --> 00:20:47,690 It was a 13 inch crop lens fed by a 16 inch sealer start from Oxford, and that was the actual instrument used and kept. 172 00:20:48,050 --> 00:20:51,050 And it's so proud to use something very, very similar. 173 00:20:51,050 --> 00:20:56,330 A 13 inch crop lens as well, said by a six inch seedless tart from Greenwich. 174 00:20:56,780 --> 00:21:04,370 And in addition, the four inch lens that I mentioned earlier on from the 1900s are clips and an eight inch 175 00:21:04,370 --> 00:21:11,060 steel stuffed so that but the latter were essentially just the backup instrumentation. 176 00:21:11,360 --> 00:21:14,020 So this is the instrumentation they got from the Royal Arch Patent. 177 00:21:14,480 --> 00:21:23,710 The intention really was to make the, shall we say, the serious measurements using the 13 inch lenses and 16 inch sealed stones. 178 00:21:26,100 --> 00:21:35,940 And this particular man Andrew Crumlin was the leader of the expedition to so bravely was from County County Antrim. 179 00:21:37,200 --> 00:21:44,220 So he actually led the expedition out to Sobral and then Arthur Eddington led the one to. 180 00:21:46,890 --> 00:21:52,620 So that was fine. They actually went took them about a month. 181 00:21:52,860 --> 00:22:04,640 By the way, if you ever get a chance to read one of these papers about the Eclipse expeditions of the past to read more like travelogues, 182 00:22:04,800 --> 00:22:15,060 they describe the boats that they got the the how, you know, the local natives not necessarily in wonderful tone sometimes, by the way. 183 00:22:15,930 --> 00:22:21,060 But it is really worth reading just to see how how things have changed. 184 00:22:23,040 --> 00:22:31,160 So this is actually the so brown eclipse equipment. And in fact, the equipment over here, this is the the 16 inch seals. 185 00:22:31,440 --> 00:22:35,220 This is the 13 inch group lens. But this is the backup equipment. 186 00:22:35,230 --> 00:22:38,880 This is a four inch lens. And the agency to start. 187 00:22:39,150 --> 00:22:42,570 So just in case anything went wrong. And of course it did. 188 00:22:44,300 --> 00:22:46,250 Right. So that was Brazil. 189 00:22:47,390 --> 00:22:58,490 And the results from this World Cup is they got a few images, but unfortunately it was cloudy and so they didn't get an awful lot. 190 00:22:59,270 --> 00:23:07,249 So brown, the large scene was not suffered from sole reason because the sun was had been shining for a couple of days. 191 00:23:07,250 --> 00:23:10,820 So that was the downside

of the beautiful weather that they had in Brazil. 192 00:23:11,240 --> 00:23:18,290 And as a result of that, the 16 and see the start produced distorted images. 193 00:23:20,280 --> 00:23:24,989 But the four inch lens. And the agency. 194 00:23:24,990 --> 00:23:35,040 The start actually produced the best results of the law, and in fact, were the results chosen by Addington in the end as the definitive answers. 195 00:23:35,240 --> 00:23:39,840 Right. And what they found was that affection for the limit of son. 196 00:23:40,020 --> 00:23:48,330 Because obviously they had to extrapolate it to, you know, using the one overall law of 1.98 plus or -0.18 arcseconds. 197 00:23:48,750 --> 00:23:59,840 And in fact, these plates were remeasured in 1979 by Harvey, and he got 1.9 plus or -0.11. 198 00:23:59,850 --> 00:24:08,100 So pretty much the same result, confirming that Eddington and Dyson had done their had done the proper job. 199 00:24:09,240 --> 00:24:12,240 And of course that's with more modern instrumentation at the time. 200 00:24:14,400 --> 00:24:21,240 And this is actually I literally did not have this up until about two days ago. 201 00:24:21,330 --> 00:24:29,160 Right. There's a there's a problem, which was that the 1919 eclipse plates from the Royal Greenwich Observatory went missing. 202 00:24:30,760 --> 00:24:40,210 All of them. Right. And this is actually from the clandestine border, the State Observatory in Heidelberg. 203 00:24:41,710 --> 00:24:51,640 Max Wolff was the director, Dan, at the time, and he was sent by Eddington a copy of one of the printed images. 204 00:24:52,180 --> 00:24:58,570 Right. So if you go on the Web and look for the 1919 eclipse and look for images of the eclipse, they're pretty lousy. 205 00:24:59,050 --> 00:25:06,550 And the reason is to just scans from old books. At the time, there are no proper scanned 19, 19 plates. 206 00:25:06,940 --> 00:25:09,970 Right. So we did come across this one. 207 00:25:10,180 --> 00:25:22,600 But in turn recently, it turns out that the The Greenwich Observer, while the Royal Greenwich Observatory at the Royal Observatory at Greenwich, 208 00:25:22,930 --> 00:25:29,800 which is now run by the Maritime Institute, apparently they held on to three plates, 209 00:25:30,340 --> 00:25:34,600 which hopefully now we'll be able to get in the next few weeks and get them scanned as well. 210 00:25:35,230 --> 00:25:43,930 But otherwise, the the the Royal Greenwich Observatory, the main set of Royal Greenwich Observatory plates, should now be in the Bodleian. 211 00:25:44,350 --> 00:25:49,570 But they're not. They're missing. And this is known by its that they're missing. 212 00:25:50,590 --> 00:25:59,290 But anyway, this is just to show you one of the print cap plates and these very faint stars here, very difficult to make measurements on. 213 00:25:59,590 --> 00:26:05,950 This is capital. Just to give you an idea of the quality of the plates from the time and this is,

of course, the name of the sun. 214 00:26:09,330 --> 00:26:17,490 So as you can see, this is Dyson's paper and Edison's paper measuring the deflection of starlight. 215 00:26:17,940 --> 00:26:21,030 They give the value here. I gave you the error is wrong. 216 00:26:21,030 --> 00:26:22,230 1.94. 217 00:26:22,620 --> 00:26:30,790 But as you can see in summarising the results of the two expedition, the greatest weight must be awarded to those obtained by the four inch lenses. 218 00:26:30,810 --> 00:26:34,380 So brown and observations seem to stop. So that's. 219 00:26:35,310 --> 00:26:42,040 So that was actually the source of the measurements. I like this bit from the newspaper at the time. 220 00:26:42,080 --> 00:26:43,420 I think it's really good. Right. 221 00:26:43,930 --> 00:26:57,560 So this is they had Dyson and Eddington made the announcement that Einstein was correct at the Royal Society in November 1919. 222 00:26:57,790 --> 00:27:02,920 And I like this bit. The subject was a lively topic of conversation in the House of Commons yesterday. 223 00:27:03,130 --> 00:27:06,220 This is Joseph L'Amour for Cambridge University. 224 00:27:06,220 --> 00:27:10,150 On arriving at the lecture before the Royal Astronomical Society last evening said he he'd been 225 00:27:10,150 --> 00:27:18,129 besieged by inquiries as to whether Newton had been cast down and Cambridge done in Cambridge, 226 00:27:18,130 --> 00:27:20,020 a clearly being done in on this occasion. 227 00:27:21,850 --> 00:27:32,310 So, of course, Eddington became very famous on the front of Time magazine at the time and spent quite a bit of time with Einstein as well. 228 00:27:33,740 --> 00:27:43,610 And so that was fine. But there was the kind of rumour that this equipment had actually gone back to Ireland at some point. 229 00:27:43,820 --> 00:27:52,610 So I decided to follow up on this because I'd become interested in her brother and I was trying to trace where this equipment had gone. 230 00:27:52,850 --> 00:27:59,870 Anyway, long story short, through the archives in the Royal Society and in the Royal Astronomical Society, 231 00:28:00,050 --> 00:28:08,210 I basically and the Royal Lodge Academy basically found out that the equipment had been sent back to Ireland in 1947. 232 00:28:09,560 --> 00:28:15,670 At the foundation of my own institution. But the Institute found a way to prevent studies. 233 00:28:16,000 --> 00:28:22,330 Was well, the first section of it, which was theoretical physics, was opened up during the Second World War. 234 00:28:22,630 --> 00:28:25,870 And so people like Erwin Schrödinger ended up in Ireland. 235 00:28:26,410 --> 00:28:32,740 And because the President of Ireland's at the time realised there was a lot of scholars and 236 00:28:33,280 --> 00:28:38,830 fleeing the Nazis and he decided to set up the institute for them to come to during the war. 237 00:28:39,910 --> 00:28:50,680 Anyway, so I actually found and in turn the sea Lestat

and the 20 foot lens buried. 238 00:28:51,640 --> 00:28:58,840 Well, in one case the instrument was buried in the basement amongst many other items in the observatory. 239 00:28:59,530 --> 00:29:10,030 Quite, quite a lot of stuff in empty territory. But in addition to see, the Star turned out to be in the garage of an X technician. 240 00:29:11,270 --> 00:29:16,429 And at some point it been sent off for him to do a bit of restoration work on it, you know. 241 00:29:16,430 --> 00:29:19,430 But anyway, we found it. It has. 242 00:29:19,430 --> 00:29:26,930 The nice thing about Grub equipment was that grub equipment has numbers on sort of boiler plate numbers. 243 00:29:28,040 --> 00:29:35,480 And fortunately, a well, grub grub, by the way, moved. 244 00:29:36,700 --> 00:29:42,550 After the First World War they moved to Newcastle and became persons who of course built telescopes. 245 00:29:42,970 --> 00:29:48,390 Up until the, up until the seventies persons when it closed, 246 00:29:48,390 --> 00:29:56,080 then they a lot of a lot of old stuff was being dumped and they had of the optics 247 00:29:56,080 --> 00:30:02,020 unit actually rescued some books from Dublin that were actually in a skip. 248 00:30:03,260 --> 00:30:05,959 And these were passed on to me because some retired. 249 00:30:05,960 --> 00:30:13,340 I was interested in Graham and turned out one of his books actually had Graham's numbers and where the instruments had been. 250 00:30:14,560 --> 00:30:23,140 So from the the number. Then I realised this was the actual seal of state and the lands had been used. 251 00:30:23,150 --> 00:30:29,860 And so brown, apart from the fact it was known the lens was 1946 inches focal length and you know, etc. 252 00:30:29,920 --> 00:30:34,090 So it was pretty, pretty definitive. Now hopefully that's the work. 253 00:30:36,760 --> 00:30:51,470 Okay. So this is the restored scene to start. 254 00:30:51,830 --> 00:30:56,390 So Madonna Observatory with the CAA in Clay did did a job on that. 255 00:30:56,420 --> 00:31:01,130 University College London restored the the Einstein hands to four inch lens. 256 00:31:01,610 --> 00:31:10,759 When I got this video from from the CAA a couple of weeks ago, I thought there was something wrong with my hard drive. 257 00:31:10,760 --> 00:31:18,560 And it turned out it was actually the noise of the governors and the see the stuff working for the first time in 37 years. 258 00:31:21,470 --> 00:31:31,100 So. So that's restored. It's now back in Dublin and in fact, we're kind of going to unveil is next week because we're celebrating, 259 00:31:31,100 --> 00:31:37,460 as Steve said, 100 years since Einstein before the general theory of relativity. 260 00:31:39,470 --> 00:31:47,420 So just to just to recap, it's this instrument here, which was the backup equipment which is now being found. 261 00:31:49,190 --> 00:31:52,399 So that was great and wonderful. 262 00:31:52,400 --> 00:31:56,840 But then that turned out to be a kind of twist to the story, which turned out to be very interesting. 263 00:31:59,310 --> 00:32:04,410 Because I realised something about the eclipses. 264 00:32:05,640 --> 00:32:13,830 So as a coastal thing you all know earth goes round the sun in 365 and a quarter days, more or less. 265 00:32:14,070 --> 00:32:17,340 Right. This is why we have the the leap year. 266 00:32:18,600 --> 00:32:22,290 And it means, for example, the solstice. 267 00:32:23,570 --> 00:32:28,760 The winter solstice. The summer solstice actually shifts over over time. 268 00:32:28,790 --> 00:32:32,780 And then, of course, you insert a leap year and then it brings it back. 269 00:32:32,810 --> 00:32:40,430 For example, in my the classic example I like Steve mentioned, I work a volt on some work in our view astronomy. 270 00:32:40,430 --> 00:32:44,500 And there's a site near Ireland called Newgrange which is actually aligned. 271 00:32:44,900 --> 00:32:53,000 It's a very long passage, but it was aligned with the winter solstice, but the winter solstice four or 5000 years ago, 272 00:32:53,000 --> 00:33:02,450 I mean, the carving dating of the scientists, 3200 or so B.C. And it's perfectly aligned for the for the winter solstice. 273 00:33:02,780 --> 00:33:10,220 And every winter solstice, you know, there's a small select party end up inside its main chamber to see the sun coming in. 274 00:33:10,940 --> 00:33:15,770 And I'm sort of wheeled up there on the 21st of December for this event. 275 00:33:16,580 --> 00:33:20,510 And, you know, there's some notable politicians or visiting dignitaries and whatever. 276 00:33:21,610 --> 00:33:27,220 But once every four years, actually on the 22nd that I'm told to keep my mouth shut. 277 00:33:29,020 --> 00:33:32,079 But then the following day, I really enjoy going up. 278 00:33:32,080 --> 00:33:39,160 And then there's some members of the public are allowed in. And I'd say this is the real solstice, not yesterday. 279 00:33:39,170 --> 00:33:42,250 Right. So you can see the pattern here. 280 00:33:42,430 --> 00:33:48,280 So basically, this is the this is of course, this is just the summer solstice, but it's the same thing applies. 281 00:33:48,550 --> 00:33:54,310 And what you have then is this oscillation, depending upon the leap year effect. 282 00:33:54,520 --> 00:34:01,000 Right. But in addition, as you also know, 365 and a quarter isn't quite right in Julian calendar. 283 00:34:01,150 --> 00:34:09,580 And there's another correction depending upon whether the first two digits of the century are divisible or not to be divisible by four. 284 00:34:09,760 --> 00:34:15,610 And so depending upon that, you either insert and and make them leap year or not, as the case may be. 285 00:34:15,620 --> 00:34:19,950 So that's why this particular pattern here. Okay, so that's fine. 286 00:34:19,960 --> 00:34:32,740 So you get this kind of drift. But what I realised was one eclipse, the 1900s eclipse that

occurred in 28th May 1900 and the second eclipse, 287 00:34:32,740 --> 00:34:38,110 which was the one that was used in Sobral and and kept, was the 29th of May. 288 00:34:38,980 --> 00:34:42,820 Right. But one was in the morning. 289 00:34:42,820 --> 00:34:48,760 The other was in the afternoon. And one, you know, it was out of step as regards to be pure effect. 290 00:34:49,630 --> 00:34:55,630 So it turns out if you put them both into a planetarium program, for example, you'll see this. 291 00:34:56,440 --> 00:34:59,770 The top one is made of 28, 1900s eclipse. 292 00:35:00,610 --> 00:35:04,320 There's capital. All right. 293 00:35:04,990 --> 00:35:10,660 And that was the one in Spain that grob one looked at and reported. 294 00:35:10,960 --> 00:35:15,100 This is so brown. Eclipse made 29th. There's capital. 295 00:35:15,100 --> 00:35:18,790 Of course, it's upside down. Remember, Brazil is in the southern hemisphere, right? 296 00:35:19,360 --> 00:35:25,120 That's why. Otherwise, within one arc minute, the sun is in exactly the same place. 297 00:35:27,310 --> 00:35:32,230 It's just a coincidence. It's nothing to do, by the way, with Saracens, etc., during different serial cycles. 298 00:35:32,560 --> 00:35:45,920 It was just pure coincidence. So what we're saying is that the same equipment had been used to observe the same eclipse. 299 00:35:47,350 --> 00:35:54,430 Right. Essentially the same. The other advantage of 1900 clips, by the way, is, of course, the sun goes through cycles. 300 00:35:54,910 --> 00:36:02,800 The 11 year the 11 year cycles are more probably 22 year, but 11 year cycles in terms of criminal activity. 301 00:36:03,400 --> 00:36:08,379 And 1900 was less active than 1919. 302 00:36:08,380 --> 00:36:12,430 So there were advantages to 1900 versus 1919. 303 00:36:16,180 --> 00:36:20,800 So let's just sum it up. The sun was in exactly the same position. 304 00:36:21,220 --> 00:36:29,920 The sky, within a minute or two of our solar activity was lower in 1900 than it was in 1919. 305 00:36:30,130 --> 00:36:35,950 The same four inch lens and sills that was used to image the sun in the same part of the sky. 306 00:36:36,760 --> 00:36:38,260 Just coincidences. 307 00:36:38,680 --> 00:36:50,650 But it begs the obvious question why didn't anybody really think of doing using photography of historical data to try and measure this deflection? 308 00:36:52,590 --> 00:36:58,670 And there was a very good reason why people were doing photography. 309 00:36:58,680 --> 00:37:01,740 They were looking for a planet called Vulcan. 310 00:37:02,840 --> 00:37:06,080 Right. So, Vulkan, let me explain that. 311 00:37:06,530 --> 00:37:09,650 And I think many of you know, you know, the history of general relativity. 312 00:37:09,920 --> 00:37:14,540 There is an effect through, for example, the advancement of the perihelion of mercury. 313 00:37:16,160 --> 00:37:21,320 And the initial explanation for this, of course, we now know,

of course, is just a general atavistic effect. 314 00:37:21,860 --> 00:37:30,079 But the initial explanation was in terms of a possible planet that was inside the orbit of Mercury and was therefore very, 315 00:37:30,080 --> 00:37:34,820 very difficult to see it even being given a name, Vulcan. 316 00:37:35,000 --> 00:37:38,480 And people started to search for Vulcan. Right. 317 00:37:39,380 --> 00:37:48,410 It's kind of ironic that the plates from the searching for Vulcan, which was purely erroneous due to the fans of the perihelion of Mercury, 318 00:37:48,740 --> 00:37:52,190 turns out to be of interest in terms of measuring the fraction of starlight. 319 00:37:53,440 --> 00:38:01,510 So that's the reason why they looked at it. And so then started looking at a number of plates from around the world from 1900. 320 00:38:02,140 --> 00:38:07,420 This is, for example, the shabu observatory's Oakland near San Francisco. 321 00:38:07,840 --> 00:38:11,710 And there's, as you can see, their capital 1900. 322 00:38:12,560 --> 00:38:16,090 Almost identical position as the 1919 model. Okay. 323 00:38:18,150 --> 00:38:22,650 But there are similar plates, Miller says, in Lake Observatory. 324 00:38:23,100 --> 00:38:29,370 There's a set in the Royal Observatory in Edinburgh as well. 325 00:38:30,470 --> 00:38:36,230 Okay. And so they all had gone off to observe this 1900s eclipse. 326 00:38:39,910 --> 00:38:44,440 But there was a suggestion to use historical plates. 327 00:38:47,400 --> 00:38:56,340 And the first person to suggest it was this man here on the left, Irwin Freundlich, or Irwin Finley Freundlich, 328 00:38:56,340 --> 00:39:05,580 as he sometimes called because he had a Scottish mother and a German German father, and he was a friend of Einstein's. 329 00:39:05,970 --> 00:39:16,470 And so back in around 1914, just before the war broke out, Einstein had predicted the deflection of starlight, 330 00:39:16,470 --> 00:39:21,090 a sort of first approximation, which we now call a sort of Newtonian approximation. 331 00:39:21,120 --> 00:39:23,430 It turns out, of course, to be wrong by a factor of two. 332 00:39:24,270 --> 00:39:33,420 But Freundlich had suggested using historical material to do this deflection of starlight measurement. 333 00:39:34,960 --> 00:39:40,290 Now, Freundlich had a couple of problems. One was he wasn't really a very practical observer. 334 00:39:40,320 --> 00:39:48,960 He was more of a theoretician. The second thing was that Struve, who was director, didn't believe in Einstein at all. 335 00:39:51,170 --> 00:39:58,510 I knew it. No, no comment. And so basically, he was not supported in this pursuit. 336 00:39:58,540 --> 00:40:05,560 He did try and go off to the 1914 eclipse and make measurements for that in Russia, 337 00:40:05,800 --> 00:40:10,060 not in the same science as the Royal Society and Royal Astronomical Society. 338 00:40:10,570 --> 00:40:16,080 And he ended up being interned, I think, somewhere around Serbia on the way to the eclipse. 339 00:40:16,480 --> 00:40:28,690 So anyway, he got out, but he he rose, in fact, to a number of observatories around the world, including Lech and the Royal Greenwich Observatory. 340 00:40:30,020 --> 00:40:40,319 To Dyson. This man here on the right, Curtis, tried to measure some historical plates. 341 00:40:40,320 --> 00:40:49,680 And then there was also an eclipse in 1917 in the US, and he actually did some work on that, but he was regarded as being well. 342 00:40:49,950 --> 00:40:54,320 Wallace Campbell, who is director of Lick, taught Curtis was a bit sloppy, by the way. 343 00:40:54,330 --> 00:41:00,870 Curtis. Some of you may have heard of the M 87 jet, so he was the guy who discovered the 87 jet. 344 00:41:01,380 --> 00:41:08,700 Photographically, he had no idea what it was, of course, at the time in the Aegean connection, but he actually discovered the jet from 87. 345 00:41:10,080 --> 00:41:20,280 So and the other complication then was that the U.S. entered the war around that time, and Curtis decided to go off the air with the U.S. military. 346 00:41:21,120 --> 00:41:26,220 So his work wasn't really completed and it wasn't done very, very well. 347 00:41:27,600 --> 00:41:36,520 Now, Dyson. As I said, Freundlich suggested to Dyson back in 1914 not to use historical material. 348 00:41:37,000 --> 00:41:45,219 I only know that because letters that are in the Lake Observatory Archive, where Freundlich writes to Campbell and says, 349 00:41:45,220 --> 00:41:55,780 I've contacted, you know, Dyson and suggested using historical material, but and that that he promised me help. 350 00:41:56,230 --> 00:42:00,040 Now, of course, when the war broke out, maybe things were a bit different at that point. 351 00:42:01,090 --> 00:42:06,850 Anyway, he never did. There's no correspondence in the audio corresponding to this. 352 00:42:09,370 --> 00:42:12,790 Then Dyson in 1917. 353 00:42:15,320 --> 00:42:20,690 Actually starts getting actively interested in measuring your general activity. 354 00:42:21,380 --> 00:42:29,150 Deflection Starlight and he prints in the monthly notices of the Royal Astronomical Society, a two page paper. 355 00:42:30,290 --> 00:42:39,170 Page one is measurements. Some historical measurements that he made on some plates from Tunisia that were in the audio archive. 356 00:42:39,800 --> 00:42:45,050 Page two I'm page one, by the way. He says, Oh, this method will clearly work. 357 00:42:46,770 --> 00:42:51,180 Right. You can see they're in black and white to page pages. This method will clearly work. 358 00:42:51,420 --> 00:42:55,440 But unfortunately, I can only measure two stars on this plate. 359 00:42:55,440 --> 00:42:59,790 So obviously that's not no good for measuring the reflections starlight. 360 00:43:00,060 --> 00:43:03,510 But the astral graphs will, will, will do the job. 361 00:43:03,810 --> 00:43:10,950 And then on page two. There is this

eclipse coming up on the 29th of May 1919. 362 00:43:11,460 --> 00:43:19,050 We have to mount an expedition to to to measure Dr. Einstein's effect. 363 00:43:20,100 --> 00:43:26,640 And that's it. He shows a sort of diagram of where the stars will be in 1919 and nothing more. 364 00:43:26,790 --> 00:43:34,810 Just the two pages. So that's actually the diagram where he's made the his initial measurements. 365 00:43:35,990 --> 00:43:41,330 But then in the process of looking into this, I realised that. 366 00:43:43,120 --> 00:43:47,290 Dyson. Only honey had three sets of plates to look at from the astronauts. 367 00:43:47,680 --> 00:43:54,240 From eclipses. It ones from, as I mentioned here from Tunisia. 368 00:43:54,600 --> 00:43:59,160 That's the one he actually measured, measured on this two page paper. 369 00:44:00,030 --> 00:44:05,370 He had the plates from Sumatra, which wasn't very good in 1901. 370 00:44:05,730 --> 00:44:11,190 And then, to my surprise, I discovered he'd been at the 1900s of kids in Portugal. 371 00:44:12,470 --> 00:44:25,340 Right. So we had those sets of plates as well. And so he was at a place called over in Portugal that would have got the eclipse first as the 372 00:44:25,340 --> 00:44:32,180 eclipse crossed the Atlantic before Rob and his party would have gotten the eclipse in Spain. 373 00:44:33,630 --> 00:44:39,480 And here's the actually pictures of the party from the Bodleian Library, which was of course, 374 00:44:39,480 --> 00:44:43,950 then it was the Royal Greenwich Observatory's Library, which has been moved recently to the Bodleian. 375 00:44:44,730 --> 00:44:49,020 So this is the party in Portugal preparing for the eclipse. 376 00:44:49,500 --> 00:44:54,030 This man here is Kristie, who is the Astronomer Royal at the time. 377 00:44:54,300 --> 00:44:57,480 And his next in command was actually. 378 00:45:00,140 --> 00:45:03,200 And then I looked at the bottles and plates and there's. 379 00:45:05,590 --> 00:45:08,830 Capital is the limit to some here. 380 00:45:09,100 --> 00:45:12,930 So you can see the. Capital there. 381 00:45:14,040 --> 00:45:17,280 Now, these plates have only got a couple of stars on them, 382 00:45:17,490 --> 00:45:24,470 so it may not have been possible for Dyson to have done it any better than perhaps the ones from S-max. 383 00:45:24,870 --> 00:45:27,420 Maybe a bit better because there are two or three other stars. 384 00:45:29,040 --> 00:45:37,260 But he could have used the eclipse planes from Central Observatory, Greenwich or Lake or whatever at the time. 385 00:45:39,960 --> 00:45:46,680 Now. Why didn't he? I don't know. Well, to 100% accuracy, but I have my suspicions. 386 00:45:47,080 --> 00:45:53,660 I think it's the best way of putting it. So the problem was World War One. 387 00:45:53,670 --> 00:45:59,850 Eddington was a conscientious objector. He said he would go to prison first before serving in the army. 388 00:45:59,920 --> 00:46:03,280 The British army. 1916, 389 00:46:03,290 --> 00:46:13,009 conscription had been introduced and in the UK actually it was also one of the contributing factors to the revolution 390 00:46:13,010 --> 00:46:19,010 in Ireland in 1916 was the fact that it looked like Britain was going to enforce conscription in Ireland. 391 00:46:20,690 --> 00:46:29,990 So by 1917, Edington was in an awful lot of trouble in terms of defending himself from not going to the war and. 392 00:46:31,830 --> 00:46:35,190 Dyson and Eddington went to Cambridge together. 393 00:46:37,840 --> 00:46:44,950 In 1918. Eddington reached a stage where Eddington had to go in front of a military tribunal. 394 00:46:46,580 --> 00:46:53,149 To explain why he was not serving in the Army. He said what he had to do. 395 00:46:53,150 --> 00:47:03,500 And this was also it was the supporting letters from from Dyson that you would have to go off and observe the eclipse to test Einstein's 396 00:47:03,500 --> 00:47:12,800 theory of relativity and that it was crucial that he go and that there would not be another eclipse like this for a thousand years. 397 00:47:15,720 --> 00:47:25,020 No, I have checked. And yes, he actually was right, apart from I think to what there was one, which is just off the Falkland Islands. 398 00:47:26,610 --> 00:47:31,020 In the 1930s where the hides were recovered. 399 00:47:32,600 --> 00:47:36,200 Right. But that would have been at sea. So, yes, we will allow not one. 400 00:47:36,350 --> 00:47:39,230 And in fact, yes, there's about a thousand years to the next one. 401 00:47:41,050 --> 00:47:51,250 Now you have to believe he never looked back 17 years, or it didn't cross Dyson's mind to look back 17 years. 402 00:47:54,380 --> 00:47:59,340 I just don't believe that. But, you know, that's so open to interpretation, right? 403 00:48:00,860 --> 00:48:11,270 So anyway, Dyson insisted I don't and would have to lead this expedition, even though he was a theorist, by the way, in his first year in Cambridge. 404 00:48:11,480 --> 00:48:17,750 If you read the stories about Eddington, he caused disaster in the first year lapse, 405 00:48:18,680 --> 00:48:22,040 and they suggest that you go off and do theory, which was a good idea. 406 00:48:23,580 --> 00:48:26,600 But then you have to ask yourself why? Okay. 407 00:48:26,600 --> 00:48:34,330 So of course, he had a clear interest in general relativity. But, you know, Andrew Cromwell and who was an observer, was sent off for, you know, so. 408 00:48:34,340 --> 00:48:39,420 BROWN Why didn't you pick somebody else from there or do you write? 409 00:48:40,350 --> 00:48:48,600 Andrew comment and by the way, never put his name to the paper. I don't know why I'm so. 410 00:48:48,820 --> 00:48:52,330 Anyway, Eddington went off to to observe the eclipse. 411 00:48:52,750 --> 00:48:55,959 And of course the results were published. 412 00:48:55,960 --> 00:49:05,230 And as I said, the results favoured Einstein's theory.

So despite the fact that Dyson had these three sets of plates he picked. 413 00:49:06,940 --> 00:49:10,000 The worst, really one of the worst ones of the three. 414 00:49:10,220 --> 00:49:13,630 Well, you know, it was kind of cloudy, so not much you could do with that. Right. 415 00:49:14,770 --> 00:49:23,530 And I still have no idea why, apart from the fact that I what I suggest was he realised from the 1900s eclipse. 416 00:49:25,730 --> 00:49:33,200 Plates and the you know, the fact that he made measurements on that, that the technique would work. 417 00:49:34,470 --> 00:49:38,580 And that may have also inspired them to realise about the 1919 eclipse. 418 00:49:40,120 --> 00:49:44,800 In the whole sort of trying to sort out the problem with Eddington as well. 419 00:49:46,590 --> 00:49:55,110 So there was always a claim, by the way, by Chandrasekhar that the only reason why Eddington was went to this eclipse was simply to avoid war. 420 00:49:55,620 --> 00:50:00,959 And a lot of people thought, well, because this was a well known dispute between Chandrasekhar and Eddington, 421 00:50:00,960 --> 00:50:04,680 that maybe it was a touch of sour grapes over all of this. 422 00:50:05,250 --> 00:50:11,940 But that may well have been something in this. So okay. 423 00:50:11,940 --> 00:50:23,370 So just to summarise, the actual equipment which had been used and proved crucial in the 1919 eclipse measurements has been found, has been restored. 424 00:50:23,700 --> 00:50:30,690 That's quite timely with next week being 100 years since Einstein proposed his general theory of relativity. 425 00:50:32,370 --> 00:50:37,170 The quip by a quirk of just a fluke chance. 426 00:50:37,380 --> 00:50:41,850 It turns out that same equipment had been used to observe an identical eclipse. 427 00:50:44,350 --> 00:50:53,580 19 years before us. And it does look like Dyson, I suppose to kind interpretation of this. 428 00:50:54,630 --> 00:50:58,620 Dyson probably realised that he would muddy the waters. 429 00:50:59,820 --> 00:51:04,140 If he'd had talked about an identical eclipse which had occurred. 430 00:51:05,630 --> 00:51:10,250 You know, 19 years beforehand that would not have served Eddington's case. 431 00:51:10,400 --> 00:51:13,400 Certainly he did not. Or he was extremely stupid. 432 00:51:13,610 --> 00:51:18,260 Right. So we've actually I mean, 433 00:51:18,530 --> 00:51:22,280 we've had a look at some of these plates to understand virtue and height in Heidelberg 434 00:51:22,280 --> 00:51:25,940 now is gathering all these plates together from different parts of the world. 435 00:51:26,450 --> 00:51:36,290 And we're going to remeasure them. And actually what our intention is that we make them available online for students of physics in 2016 to 436 00:51:36,620 --> 00:51:43,340 actually measure the deflection of starlight from themselves with the 1900 plates and the 1919 plates, 437 00:51:43,640 --> 00:51:47,840 hopefully the ones in the audio are still alive. Okay, so thank you very much.