It was raining fairly heavily almost until I left the hotel but had just about dried up, unfortunately the road conditions were atrocious, a broken down truck combined with the general traffic nearly doubled the journey time from Gravesend. I’d booked car parking a while ago but it’s at the bottom of the hill near the Maritime Museum - thank goodness for the scooter!
Looking up to the Observatory
The first hiccup of the day was that the lift at Flamsteed House, where many of the displays are, is broken, actually in the end that only gets you onto the ground floor and it was so busy the scooter would have been a nuisance. A pleasant young lady pointed me to the buggy park which has a nice convenient iron railing to chain the scooter to (and has a canopy so if it did rain again it wouldn’t have mattered) and I was happy then to wander round.
Inevitably there were a lot of school and tour groups so at times I had to pick my moment to see things, I wasn’t too bothered about the displays on the families of the Astronomers Royal, what I was really there for was to see information on the Longitude Problem - see below.
H1 - Harrison’s first attempt at a timepiece to solve the z Longitude Problem.
H4 - The first marine chronometer.
A marine chronometer from the Portuguese merchant ship the Ferreira, now better known as the Cutty Sark.
Greenwich is inextricably linked with time, although the global standard is no longer Greenwich Mean Time, and there were several displays about how ti me was transmitted around the country, including by electric telegraph and later by radio waves from near Rugby.
A Regulator Clock and two electrically driven slaves.
As things had quietened down a little when I went back outside outside I went and took the obligatory photo on the Meridian line then unchained the scooter and headed through the shop to the exit, only then realising I’d missed part of the overall tour.
Right foot in the West, left foot in the East.
It was definitely coffee and cake time though so I headed down to the cafe first then went back in to the observatory area and chained things up again. The main thing I’d missed was the large Meridian Telescope - had I realised the exit from this involved a two storey iron grate spiral staircase I might have been less enthusiastic about seeing it, my irrational fear of heights kicked in but I coped.
The London skyline from the observatory.
With the observatory ticked off the list, and with time to spare, I scooted back down the hill to the Maritime Museum to make a start on looking round there (I’ll be back tomorrow). I got round a few of the exhibitions, it’s a little disjointed, and had some lunch before deciding I was tiring and heading back to the hotel - a much quicker drive than in the morning.
This 1930s speedboat is exquisite.
This stained glass was in the Baltic Exchange in London, one of the main clearing houses for information and contracts in merchant shipping.
The Longitude Problem
I’ve simplified this considerably (I’ve got whole books on the subject) and I think I’ve got the details correct!
It was relatively easy for sailors to work out their Latitude (how far North or South they were) but Longitude (East or West) is difficult. Prizes of up to 20,000 pounds (several million today) were offered by the British Government for solutions to the problem, ignoring the more outlandish ideas there were two main solutions.
Common to both methods was measuring angles in the sky; this needs some form of accurate instrument. Eventually the earlier land based telescopes and quadrants (a quarter of a circle) developed into hand-held octants and then into the sextant (a sixth of a circle). This latter has a small telescope and a system of mirrors that superimpose the images of the two objects you’re measuring. You simply move one of the mirrors in an arc and when the objects are aligned you can read off the angle. I have the Brother‘s relatively cheap sextant at home, I did mean to bring it with me as I need a decent horizon to adjust it and I’ll be by the sea later in the week.
The first method, typically favoured by astronomers, involved charting the position of the moon relative to the stars; to do this you needed good visibility and knowledge of the heavens to take accurate measurements, some complex mathematics and extensive tables, and you had to do this on a moving ship! There were ways of doing this on land* but not at sea.
The second method required very accurate time keeping, but was relatively simple. The easiest way to find your position involved a noon sun-shot, measuring the angle between the horizon and the sun at its highest point (the local noon) and noting the exact time (at a known place) that this occurred. With a bit of calculation, and some nautical tables, the angle gives you your latitude and the time gives you your longitude. For example if your local noon is at 13:00 Greenwich time you know you are 1 hour to the West so 360 degrees divided by 24 which is exactly 15 degrees west of the Greenwich Meridian. The biggest problem is knowing the time at your fixed place though - in the early 1700s the most accurate clocks available used pendulums but these need a stable platform, put them on a ship at sea and they’re next to useless.
It took a Yorkshire carpenter turned clock maker, John Harrison, 4 attempts over many years to finally produce a reliable and practical Marine Chronometer. He was eventually awarded over £23,000 from the prize funds after petitioning King for the final payment. For 300 years, from the late 1700s, a sextant and chronometer were the main tools for navigating at sea, and in the air, when you couldn’t see land until the development of electronic aids including GPS.
*The Mason Dixon Line in the US was surveyed in the 1760s by Charles Mason, an astronomer from the West Country, and Jeremiah Dixon, a surveyor from County Durham who learnt his trade in his father’s pits, using astronomical techniques.
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