Longitude

"Finding the Longitude" - A fresh look at the story of John Harrison versus Nevil Maskelyne and of position fixing at sea.

[@PifflePrattle]

People like stories involving heroes and villains. I'm sure there's a moral in this excellent production applicable to a wide range of subjects.

[@EricBishard]

I'm so glad I stayed for the end, what a nice little bonus to see those two beauties

[@steveragnall6249]

Thanks Eric. I'm lucky to have them!

[@MrMidiman]

Great film Steve, really enjoyed it. I think your perspective on the Maskelyne Vs Harrison relationship is spot on. I can't help thinking the John Jeffrey's watch/contribution is significantly underplayed too.

[@steveragnall6249]

Many thanks for that. Glad you agree. Wish I could find an image of Jeffrey, unsung hero that he was.

[@robertfarquharson2878]

Thanks! I’d only heard of the Sobel style narrative of Harrison as the underappreciated genius. Very interesting.

[@heinpereboom5521]

Wonderful explanation of this history! Here again it turns out that mechanical things are much more complicated than they seem. Even the Cristiaan Huijgens had not understood that a pendulum clock with a gimbal suspension and a weight below only makes the clock hang vertically and does not work at all in a ship, because of the displacement of the suspension point in the ship when it swings. It is very special that such beautiful clocks could be made long ago, they are precious possessions.

[@AHBdV]

A fantastically nuanced story. That's the problem with books and TV about one person... there always this tendency to over dramatise it, and make it a battle between good and evil. Its good to have someone show some other perspectives.

[@johnnyarsenault9124]

Really appreciated your presentation of your copies of time keeping as to have a physical idea of their size. Beautifully crafted they are 👌❤️👍

[@steveragnall6249]

Thanks Johnny.

[@MK-ge2mh]

Wonderful work you've done! I've enjoyed this immensely, sir. I too agree with your take on their relationship. Maskelyne was simply being pragmatic and worked on the solution from another angle. It was important that each solution complement, verify, and validate the other. Both men truly understood the import of finding a solution, as many lives depended on such. I've read through book and seen the movie. I've had my doubts that men of such education and charged with obtaining a solution to so serious a problem, would scoff at Harrison even after such progress he made.

[@steveragnall6249]

Many thanks for your comment. Glad you agree!

[@stephenarbon2227]

A beautifully clear & concise documentary.

[@steveragnall6249]

Thanks very much!

[@hippopotamus6765]

Excellent narration, most informative.

[@torreyintahoe]

Great video. Very informative.

[@jacksondouglas5694]

Great video. I had my first encounter with the longitude problem when I was a teenager trying to measure the longitude of our small amateur observatory, here in Chile. I´m an admirer of John Harrison !

[@steveragnall6249]

Thanks for sharing! Glad you enjoyed it. Best wishes, Steve

[@FredMiller]

Wonderfully presented. As a student of Celestial Navigation and an X USCG sailor I can appreciate what these gentlemen did to try to solve the Longitude problem!

[@steveragnall6249]

Thanks Fred!

[@peterhall6656]

What a ripping yarn! I read Sobel's book and wondered about all the skullduggery that would have gone on given the stakes. Most students today know nothing about spherical geometry but in those days they had to perform complex trigonometrical calcuations by hand with log tables. Imagine doing that on a rolling ship in bad light etc etc. This was an astonishing time when men did things with their bare hands. I am gobsmacked by the able seaman who manufactured a spring. What a guy!

[@steveragnall6249]

Thanks Peter. i'm a sailor and can't even use a sextant...I have one, but at sea I never seem to get the sighting right. Thank heaven for GPS!

[@rysacroft]

Many years ago, before GPS, I set sail on on a yacht form Falmouth UK bound for the the Canary islands and then on to the Panama canal. Our destination was the West west of Canada. But due to the Southey storm force wind we had to turn around. In those days was a system were they would transmit Morse code from stations either side of the English channel.Using a direction finder, in theory, you could work out your position. After three days of being blown North we were completely lost. It's a miracle that we got back!

[@hippopotamus6765]

I had a similar incident in the south pacific many years ago. A fortunate outcome but a valuable lesson on how easy it is to muck it all up and compound the errors.

[@evanofelipe]

I first discovered Rupert Gould’s book on the Determination of Longitude in 1975 and was immediately captivated by the extraordinary story of John Harrison’s immense struggle for recognition of his genius and overdue payment of Queen Ann’s £20,000 reward. I later read Dava Sobel’s book ‘Longitude’ it is a good read, but lacked the ‘hands on’ experience and personal commitment of Gould. Without doubt, apart from being a thing of beauty Harrison’s invention helped save the lives of countless sailors before the invention of GPS. It’s a story that deserves to be told through time immemorial.

[@tonymercer7759]

Sobel's book is eminently readable and most suitable for the those looking for a good explanation of and solution to the longitude problem

[@benwilson6145]

My favourite book review was" Dava Sobel had a lot of Latitude with Longitude"

[@willlockler9433]

Excellent. Thank you.

[@steveragnall6249]

Thanks Will!

[@MrHerbsandspices]

An awesome informative video, thank you.

[@steveragnall6249]

Thanks for that. much appreciated.

[@The-Cosmos]

Thanks a lot.

[@charlesstevens8913]

An amazing history lesson! Thanks you for rounding out my knowledge of the 'search for the Longitude.' BTW, the documentary entitled "The lonely halls meetings' provides a very interesting summary of the history of the efforts to went into the GPS system operational!

[@steveragnall6249]

Many thanks, Charles. I'll look up that documentary.

[@daniyalrazakazmi7249]

I just finished reading the book!!! It's fascinating story! I'm currently doing Masters in GNSS and I feel more appreciation to the longitude problem!

[@steveragnall6249]

Excellent Daniyal! Thanks for sharing and good luck with your Masters.

[@007EnglishAcademy]

Excellent. Very well done, indeed.

[@steveragnall6249]

Glad you liked it!

[@jimadams7765]

Very nice vid. As a schoolboy I used to spend my lunch-hours playing football or visiting the National Maritime Museum and The Observatory. I loved watching the large clocks - the movements were beautiful and mesmerizing. And at that time, they were all fully working. (The "pocket" watches were less interesting to me - no visible moving parts as far as I remember).

[@steveragnall6249]

Thanks for sharing!

[@Jm4steam]

Very interesting. I think the movie Longitude did a decent job portraying how longitude was resolved.

[@martincarroll8637]

Loved both the book and thoroughly enjoyed the saga on film.

[@steveragnall6249]

Thanks Martin.

[@ekremyahsi3070]

Thank you

[@MrNerdy0123]

The two part series of Longitude dramatizes the relationship of Harrison and Maskelyne as good v bad, this video clarifies what was actually the reality. Scientists want the end goal to be achieved and realise it needs to be a joint collaboration.

[@MontyVierra]

This debate and the book/film to which you are responding are both new to me. I think you've done a superb job of explaining the controversy in language that is both accessible to the layman yet scholarly in tone and in content. The visual presentation is also excellent. Thank you!

[@steveragnall6249]

Thanks for your kind comments, Monty. much appreciated.

[@pforce9]

thank you for your reseasrch and presentation.I am always anxious to know the real history. they didn't go into details in the movie about Maskelyne's system but I like the part about not carrying over errors.

[@steveragnall6249]

Thanks for your comment pforce9

[@pforce9]

@@steveragnall6249 In the 1980's Bernard Montressor came through the Bay Area and offered a celestial navigation course which I took aboard his sloop "Joshua". At one time, I had the six sets of HO 229 books and the seventh, which I forgot the number, so I have an idea of what goes into calculating a position. It seems to me that they both had to use the same tables once Maskelyne had determined the local time which he did by lunar observation. Harrison on the other hand has a host of corrections that needed to be made. Since the earth is not in the center of the universe, there is a correction for that and since he has Greenwich time, he has to make a correction for that, and some other things I forgot. Seems to me it might be a wash on the time spend on the methods. One more thing. That chair was made to look stupid, but Sir Francis Chichester had a gimbled chair inside his yacht. If the inventor had just removed the 400-pound weights and used the weight of the occupant, the chair might have worked fine.

[@steveragnall6249]

@@pforce9 I've always had difficulty in using a sextant - perhaps I should have had one of the gimballed chairs! Incidentally, you're probably aware that non of the chronometers was completely accurate - they either gained or lost time each day, so had to be regulated to ascertain their daily difference, which then had to be factored in to every calculation.

[@andypdq]

7:09, that's an octant, the sextant was introduced to allow longitude to be established by the Lunar method.

[@javiersanchezdelabarquera4879]

Hermosamente relatado. Mis respetos. Y además le felicito por ser el merecido poseedor de dos envidiables replicas de relojes históricos.

[@steveragnall6249]

Gracias por tu amable comentario, Javier!

[@RollaArtis]

Thanks for this potted history of the Longitude, but you didn't mention John Arnold who was the inventor of the marine chronometer from C1780 onwards. Harrison's watch was a completely different and complex machine which as you point out could not be produced in numbers.

[@steveragnall6249]

Thanks for your comment. I'm hoping to include Arnold in a further film. He was another great guy but I'm sure you'll understand that the main thrust of this film was to "adjust" people's view of Maskelyne and the supposed "fight" by Harrison to get recognition.

[@RollaArtis]

@@steveragnall6249 Quite - unfortunately there are many people who have read a certain book and think it's all fact, even though it's just a concocted mix of fact and fiction. Look forward to seeing your future projects.

[@charlesgantz5865]

Interesting take on issue of whether there was real competition between Maskelyne and Harrison, and whether this effected the awarding of the prize. I'm not sure what is correct, but it is an interesting take. I would have to say that it wasn't necessary for the clock to be accurate for a three year, or long, voyage. The problem that Maskelyne and Harrison, and others, were trying to solve was the determination of longitude at sea. The determination of longitude on land was a fairly simple proposition, and most large ports had observatories to determine that. Then by doing their noon sights, on land, they could accurately determine the time difference between them and Greenwich. The ships could then determine the errors in their clocks. One of the important functions of Naval ships was to determine the longitude of various ports and islands. To do this they brought along their own astronautical instruments. The important thing was that the clock accumulated errors changed in a deterministic way. Harrisons big contribution to that, as you mentioned, was introducing the bimetallic strip, which minimized fluctuations in accumulated errors. These were introduced in H3. Clocks before that had wildly changing errors introduced by differences in temperature. Of course, the other important thing was that the clock be reliable. If the clock stopped, then you had other problems.

[@steveragnall6249]

That's right Charles. Thanks for your comment.

[@hans-uwearnold2281]

Sehr interessant! Gruß aus Deutschland! Hans Arnold

[@benwilson6145]

An error, you do not take a single sight at Noon to determine your position. You take one in the morning and transfer this position line to the cross the Latitude found at Noon to get your position.

[@toml.8210]

Is there anyone selling clock kits any longer? Quartz movements are for the garage or the basement.

[@catherineburton195]

38-115nm, not 60-180nm. The formula is change of longitude in minutes times the cosine of the latitude. So 3° of chlong = 180’ x 0.643 = 115.7nm.

[@johnhillside9105]

If the works were comparable to the 🌎 Earth's Day,...then a record of travel existed in the dial of the Chronograph. Setting a Noontime at London, Longitude 0° meant that all changes are shown concerning distance by measurements of the Noontime London Longitude!! It's so neat.

[@TesterAnimal1]

What?

[@gauravk.s.326]

🙏🏿Harrison 's notion as 360/24=15* being gr8,however the land water uniform distribution all across the planetary realms could advocate for greenwich shift ; Eventfully wonder if passes through my native country if measured correctly or who knows suitably being Ukraine !

[@roytofilovski9530]

Seems to me the truest hero here is Mr. LeRoy.

[@mrxmry3264]

9:08 thanks, bob! 31:05 i have to correct you there. GPS satellites are not in geosynchronous orbits. IIRC they are about 20000 km up (geosynchronous is 35800 km up).

[@steveragnall6249]

Well spotted. Minor blip, but you know what I mean!

[@phmwu7368]

Interesting summary, pitty of the animation showing the Earth globe spinning in the WRONG direction at 30:50

[@rodbennett4790]

G'day Steve, An important aspect of the story is missing. The detail of the timeframe and the battles that Harrison had to fight in order to be "very well paid".

[@steveragnall6249]

Hi Rod, i think that's the point - we only have William Harrison's story that they "battled" to get money. The BoL were supportive but John kept his work close to his chest. "Just keep giving me the money and when I'm ready I'll show you what I've done" sort of thing. We accepted Dave Sobel's view because we have an almost built-in distrust of Quasi-Govenmental organisations (usually quite rightly!) like the BoL but, looking at it calmly, they were spending public money and had to be sure it was well spent. The evidence from our Longitude project seems to indicate that Harrison wasn't treated badly - or as badly as Sober wrote.

[@sivasurrey]

The quote about on the shoulder of Giants was made by Einstein, not Newton

[@steveragnall6249]

Sorry, You're wrong. “If I have seen further,” Isaac Newton wrote in a 1675 letter to fellow scientist Robert Hooke, “it is by standing on the shoulders of giants.”

[@greggweber9967]

Could a Lead Line tell them that they were safe if there was no loss of tension at shallower lengths? When it touched something would be the time to slow down and feel your way into port.

[@steveragnall6249]

The lead line did two basic things: It told you depth of water beneath you of course, which you could relate to any chart you had of the area (or at least know if you were heading into shoaling water) and secondly, if the lead was "charged" with tallow filled in the end, it would pick up a sample of the sea bed, showing whether it was sand, broken shell, mud, etc. This could also indicate where you were. If you were in any doubt as to the waters ahead, you would keep casting the lead and, if moving into shallowing water, you would most likely start to take the way off your ship by taking in or backing sails. Alternatively, you might change course and take the vessel back into deeper water. Hope that answers your point.

[@benwilson6145]

You are partially right, the 100 Fathom Line / 200 Metre line is a very distinct sounding line that was used by Navigators.

[@karhukivi]

By the time it touches something it might be too late to avoid a sharp spike of volcanic rock coming up from a 4 km ocean bottom!

[@benwilson6145]

@@karhukivi So lets discard soundings because one in a million it might be misleading! Very logical!

[@karhukivi]

@@benwilson6145 Around the Canary Islands, the bottom rises up very steeply from 4 km. If you relied on soundings alone, you might get a surprise. The English Channel is a different proposition.

[@dipling.pitzler7650]

I think there is a mistake at 4:00 , 10000 pounds for a Measurement within one degree, not one minute !

[@steveragnall6249]

Correct. You win tonight's star prize which is...nothing. Yes, I said minute instead of degree - well spotted. Incidentally, if you want to be exact, 1 degree = 54.6 miles, but let's not quibble about it, ha ha.

[@The-Cosmos]

Leonhard euler was born in 1707!

[@benwilson6145]

The beginning statement about Shovells error was wrong. You state it was between 1 and 3 degrees of Longitude and say its 60 to 180 miles, you don't state what type of miles, I assume Nautical Miles. One degree of Longitude at the Equator is 60 nautical miles. At the Pole One Degree of Longitude is 0 Nautical miles. Not sure what latitude the Scilly is, I estimate at 50 Degrees using mental maths at the length of a degree of Longitude being about 40 Nautical miles.

[@philmoore71]

interesting ... but noon/sun being at its highest isn't really correct. I live in Estonia and 'timeandate' shows it is at around 12.21

[@steveragnall6249]

Thanks Phil. Here's the "official" description: "In terms of solar time, noon is the moment when the Sun crosses the local meridian and reaches its highest position in the sky, except at the poles. This version of noon is also called solar noon or high noon." It was always accepted as the start of the naval day because it was observable, unlike 12 midnight!

[@FrodoOne1]

Estonia (like every country) has one (or more) "Time Zones". across the whole country. For Estonia, this is 2 hours ahead of GMT/UTC (or 3 hours for "Summer Time") The "Time Zone" is accurate only every 15 ° of longitude. Any place in Estonia East or West of 30 ° East longitude, will have an "inaccuracy" in the "local" time. Time Zones were developed in the 19th Century because Railways needed Time-tables which could relate to all points on their route. (If each Town used its "Local Time" these time-tables would become incredibly complex and subject to misunderstanding.) If Noon in your location is 21 minutes ahead of the Estonian Time Zone, that location is 5.25 ° East of that longitude and is at 35.25 ° East Longitude..

[@user-iv7pl2uo7q]

Fascinating & educational. To be accurate; however, the term "dead" reckoning is incorrect. It is "ded" reckoning, based on the word, "deduced":. Through a series of log checks, windage, sun or moon positions, etc a best guess could be made of position.

[@Tmanaz480]

Check the OED on your next library visit. Earliest use of "dead reckoning": 1613. Earliest usage of "ded reckoning": 1931.

[@andretucker3810]

Is Elmira and cape coast in guana lining exactly north to Portsmouth England on purpose you think to make it easy to get there for the slave trade ?

[@roysokolowski7234]

Good video but I have one constructive criticism. Your introduction graphics are way, way too long and detract from an otherwise good presentation.

[@steveragnall6249]

I think you're right Roy. It's partly because I'm a musician as well and don't like to break up a piece of music too much! And I was enjoying myself with the graphics....

[@MrKen-wy5dk]

720p upload in 2021???

[@steveragnall6249]

You're lucky you got that, ha ha.I still watch B&W films! it has no relevance to the content however...

[@ioanstef1983]

All Inspiration Comes from God, yet few are/were Grateful!

[@charlesgantz5865]

Praise the Lord and pass the ammunition.

[@neiloflongbeck5705]

Harrison's fault was being better than so-called betters.

[@steveragnall6249]

That's the perception that was put out a while back Neil, but it doesn't quite fit the facts as we now know them. Astronomer Royal Edmund Halley was definitely on his side, putting him in touch with Master Clockmaker George Graham to help put Harrison's ideas into a coherent proposition. The BoL then accepted those ideas and ran with them, bankrolling him through development. Some of the BoL perhaps looked own on Harrison but not Lord Morton or Nevil Maskelyne as Dava Sobel would have you believe. The Royal Society even enrolled his son and there seems to have been less snobbery at that time between inventors, scientists and the "Upper Classes' than you would think. So much detail came to light when we began the "Longitude Project" some 15 years ago. Up until then I was of your opinion.

[@neiloflongbeck5705]

​​@@steveragnall6249 Maskelyne had a clear conflict of interest that in today's society would have automatically disbarred him from judging the work of all others in the seeking if the longitude problem. The fact that Maskelyne didn't claim any moneys from the Board of Longitude is neither here nor there.as for Harrison being paranoid about industrial espionage, well so was the British government. At least 2 of the test voyages for Harrison's timepieces were cancelled due to war. A fact you have failed to mention. When a written description of Harrison's timepieces was published all royalties went to the Astronomer Royal, a certain Neville Maskelyne, of the grounds that these timepieces belonged to the government as Harrison had been paid for them by the Board of Longitude. A fact that is note worthily missing from your presentation. This means that from your total of payments to Harrison need to be be properly explained. Which I doubt you will ever do, as your bias is clearly seen. Harrision received around a third of the amount stated for his work on H2, H3 and H4 before being awarded £10,000 for H4. As for the Lunar Distances method the need to do the calculations that took up to 3 hours to perform meant that unless at anchor you would only have as rough idea where you were once the calculations were done. Whereas, with the chronometer you knew within seconds of taking the reading. Both methods had errors in taking the readings, which you also failed to mention, and not just with the loss or gain of time of the chronometer.

[@steveragnall6249]

​@@neiloflongbeck5705 i don't think I'm biased, Neil, I still think Harrison was a genius. My case is that the full story still hasn't been told and much left unsaid, and is based on our work, part of which can be followed (as a staring point) at cudl.lib.cam.ac.uk/collections/longitude. As Astronomer Royal, Maskelyne couldn't have recused himself (if such an idea would have held sway in the 18th century) because it was one of the prime purposes of his job and, on that premise, might have had to recuse himself from publication of the Lunars. He hasn't been given enough credit for the nautical Almanac. Maskelyne was custodian of all the instruments and timepieces at the Royal Observatory and was certainly not against the development or use of timekeepers at sea, which has been the common perception. Please note, I didn't say "paranoid" about Harrison, nor would I, but he certainly wasn't a collaborator like other watchmakers, except for getting John Jeffrey to make parts for him. No, I didn't mention "voyages cancelled by war", neither did I mention all the other other voyages for testing, such as the royal Navy test of Christiaan Huygens & Bruce's marine clock on HMS Reserve back in 1663, for instance, as they're not essential to the story I'm telling here. If you want to be nit-picking, you could say I should have detailed exactly when each of the BoL payments was made to Harrison -I'd thought of doing that and it would have been of interest, I'm sure, but you simply can't include every piece of information in a relatively short video. Just a note re the royalties you mention, please check the accounts - you'll see they went to the Astronomer Royal as trustee for the royal Observatory and were not used by Maskelyne himself. It did seem mean that Harrison didn't at least get part of them. He was a wealthy man, though, and not the underpaid and overlooked chap many consider him to be. Your final paragraph - I agree, and if my video hadn't already been too long I'd have put in much more detail (it's almost worth a second film) but most people would have been fed up by then! Incidentally, I did mention errors in brief. I never really mastered taking readings by sextant - how they could be accurate on a heaving deck - mine is just gathering dust! Thanks for your comments.

[@neiloflongbeck5705]

@@steveragnall6249 your source is not available and as such cannot be used to support any argument. The royalties on the book on Harrison's book according to all online sources that are readily available and reliable show all went to Maskelyne. After all at that time all of his timepieces, including H4, and all notes and drawings had been surrendered to Maskelyne. And 2 further copies of H4 were ordered to be made by Harrison without reference to either H4 or his drawings or notes. Hardly a fair test for a man in his 70s. Unfortunately under the terms of the original Longitude Act Harrison's H4 met all the terms required to show full compliance. Everything else that was done was in order to keep Harrison in his proper place. Your obfuscation of the truth of the payments made to Harrison is a clear sign of bias against him. You've made him out to be a greedy money-grabber, when all sources show that the monies received where for the work he was carrying for the government. The same is true today when one of the weapons manufacturers sells a new weapon to the government, payments are made to develop the weapon. And yes, Maskelyne should have been not allowed to sit in judgment as from all sources that are available on line he was biased towards the astronomical observation methods, which would only be reliable when the sky was clear enough to make observations, provided you had at leasty 3 hours to do the calculations and didn't mind their inaccurate results. If Maskelyne had been a man of honour as you have made him out to be then he would have allowed someone else yo sit in judgment. You mean the Bruce-Ooterwijck clock whose performance reports were all, according to the National Museum of Scotland, made up? As for Harrison's H1 not performing well at sea, well how was a man who had never spent time at sea to know that ships move in roll, pitch and yaw? By your commentary you make Harrison out to be an idiot instead of merely ignorant.

[@steveragnall6249]

​@@neiloflongbeck5705 i double checked the link - it works. When you've checked all the sources, you may change your mind, though from your comments I doubt t it. Please don't put YOUR words in my mouth, and do not misquote me. I repeat, as i said in the film and in my answer to you: Harrison WAS a genius. You may consider him or maskelyne a mineygrabber - I do not!

[@MrKen-wy5dk]

Only 720p upload in 2021??? Forget your channel.

[@TesterAnimal1]

Because that’s the important thing. 🙄

[@georgesluker7113]

With all the research and effort that went into this informative product, it is regrettable that a narrator with a more distinct and clearer pronunciation was not used. Very difficult to understand what is being said without constantly replaying sections that are muffled and the words seemingly swallowed. With so much effort needed to comprehend what is being said, concentration on and retention of the facts is diminished. Sort of like looking at a beautiful vista through foggy glasses; just cannot appreciate all that is before you.

[@fredtromp9497]

Just turn on closed captions if you can’t decipher the accent. I’m hard of hearing and the cc worked just fine

[@ilanpi]

I'm afraid you don't quite know what you're talking about. 1. If the weather was worsening, then how would they be able to figure out longitude, which would require celestial observation even with a functional marine chronometer. 2. In Antiquity, Polaris was not the pole star, due to precession of the equinoxes. 3. According to the leading scholar of ancient mathematical astronomy, Otto Neugebauer, The Early History of the Astrolabe. Studies in Ancient Astronomy IX, Isis , Aug., 1949, Vol. 40, No. 3 (Aug., 1949), pp. 240-256, the earliest confirmed astrolabe belongs to Ptolemy ca. 150 B.C., with the the stereographic projection possibly known but not fully understood (preservation of circles and angles) by Hipparchus ca. 150 BC, but previous knowledge of this by Apollonius or Archimedes (not Eratosthenes) being completely conjectural. Since you are continually making stuff up in this video, I stopped watching at this point...

[@steveragnall6249]

I'm sorry that you feel that way but unfortunately, as you didn't bother to watch further, you would have seen that I addressed all those points! Firstly, you must recognise that this talk is primarily about Harrison, Maskelyne and the BoL. and not about ancient Astronomy, which I only outline as as preface. I also point out that Thales of Miletus was running navigation classes using Ursa Minor in 600BC. Additionally, our most recent research gives that Eratothenes was possibly further forward with a mechanism similar to the Astrolabe than previously thought - but you don't note the qualification to this in my remark. It made me smile when you say that this talk was made up - it is in fact a result of working with the NMM and Greenwich Observatory, who I'm sure will like your comments. Whilst I am happy and willing to receive informed criticism, I wish you'd checked your comments before rushing in - And a more polite and considered message would have been greatly appreciated.

[@MontyVierra]

@@steveragnall6249 Your reply is a perfect example of what is meant in the phrase "gentleman and scholar."