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by popular television presenter Adam Hart-Davis

Thomas Romney Robinson

The child prodigy who became Director of the Armagh Observatory

Armagh Observatory was built in 1790.  The Director for almost 60 years, from 1823 – 1882, was a man of exceptional versatility and vitality, even among my heroes.  He made significant contributions to astronomy, meteorology, electricity, magnetism, turbines, air-pumps, fog signals, and balloons.  He even stressed to ladies the importance of chemistry!  In an address to the Royal Irish Academy in 1852 he said “The person who cultivates only one branch of science cripples his mind, and does himself an injustice.”  His name was Thomas Romney Robinson.


Thomas Romney Robinson was born in Dublin on 23 April 1792.  He was a child prodigy, reading avidly by the time he was three, and having a book of his poetry published when he was only 13.  He became Rector of Enniskillen, and then Director of Armagh Observatory when he was 31.


The most worthy thing he did was to compile a catalogue of the positions of 5345 stars, a huge task – ten years of work for him and his assistant Mr Neil McNeil Edmondson.  When it was published in 1859 it won him the Royal Medal of the Royal Society, and he said proudly “Already it has taken its place among the standard catalogues of reference.”  But Mr Edmondson said “The fact is, Doctor, it has made old men of us”.

In 1849 Robinson read a paper in Belfast about his observations of the Moon.  He made a nuber of statements which show the depth of his understanding:

  • We see only one side of the Moon, because it turns on its axis at the same rate as it revolves around the Earth; so the same side always faces us.

  • It has no atmosphere, because stars going behind it disappear suddenly, whereas if there was any atmosphere they would disappear slowly.

  • Things on the Moon are light and spongy.A body weighing 6lbs on Earth would weigh only 1lb on the Moon.

  • From the length of the shadows we know there are cliffs on the Moon 25,000 feet high, while on Earth there are none more than 500 feet.


Solving Wind Problems


Robinson was always interested in anything that might upset his astronomical abservations.  Railways, for example; they shook telescopes and by using his influence in the House of Lords, Robinson managed to prevent people from building railways, not only at Armagh, but also at Greenwich and Oxford.


Wind also rocked the telescope.  What was the best way to measure wind speed?  After much thought, and consideration of various types of apparatus then used, he invented the cup anemometer.  He reckoned that hemispheres would be efficient and easy to reproduce – anyone could make them.  He experimented, and decided that four arms were better than three or five.  He calculated that if there were no friction, the speed of the cups would be exactly one third of the wind speed, which turned out to be correct.  And finally this elegant machine does not have to be turned round to face the wind.  It works just as well wherever the wind actually comes from.


This was such a good piece of thought and design that no one has bettered it yet.  You’ve probably seen them in airports; meteorologists all over the world use cup anemometers, although they often make them with three arms.

Rockets For Longitude


But what really endears Robinson to me was the way he set out to find out where he was.  At the 1834 meeting of the British Association for the Advancement of Science in Edinburgh, and at the 1838 meeting in Newcastle, he and others agreed to measure very accurately the longitudes of Cambridge, Oxford, Dublin and Armagh, basically to check the maps.  I find it hard to think about this – we now assume that our maps are dead accurate – but 150 years ago there was some uncertainty about the exact positions of places.  So they wanted to measure their longitude, and they wanted to do it with two varying and different methods.


They persuaded the famous clockmaker, Mr E J Dent, to visiot them with 15 chronometers.  They were all synchronised at Greenwich; then Mr Dent carried them in a wooden box on his knee, 500 miles by train in England, 275 miles at sea by steamship, and 190 miles by stagecoach in Ireland.  The whole journey took only a week, being performed as Robinson remarked, “With the marvellous rapidity of modern improvement.”


But he also wanted to use direct observation; so his second method was to set up a signal that could be seen from both Armagh and Dublin at the same time.  Then they could be sure that their clocks were exactly synchronised.


There isn’t a mountain high enough to be visible from both places, but the highest mountain between Armagh and Dublin is Slieve Gullion, and from Slieve Gullion they could fire rockets high enough for the explosions to be visible from 18 miles away in Armagh and 51 miles away in Dublin.  He sent up his son to organise the rockets, with assistance from Lieutenant Thomas Larcom of the Ordinance Survey, who provided them with maps, tents, and most important, rockets.


They set up camp on the mountain on 13 May 1839.  The Rector of Forkhill provided remarkable hospitality, even for Ireland, including food and two policemen, in case of trouble.  The only trouble came from the weather; as it snowed, and for two whole nights that week they couldn’t fire any rockets.


Robinson sat in the observatory in Armagh; his friend William Rowan Hamilton sat in Dublin, and they both had to measure as accurately as possible the time of the rocket bursts.  Robinson also trained three assistants, by getting them to write down the times of shots from a flintlock pistol.


Robinson sat in the dark by his telescope, and every now and then looked at the precise grandfather clock, by the light of a candle, and he counted the seconds in his mind.  “Five past one, and ten seconds, eleven… 12… 13… 14… 15… 16… 17 FLASH – there it goes – about 17.4 seconds – write it down.”


They started firing rockets at 10 o’clock at night – obviously they could see the signal better in the dark.  They fired 15 rockets the first night, at five-minute intervals, 13 the next night, and more at the end of the week.  Each rocket provided one precise observation in Armagh, and one in Dublin.


They both knew their local time accurately, by observations.  After watching the rocket explosions they could synchronise their clocks, and measure precisely the difference between local time in Dublin and local time in Armagh.


The result of this heroic set of experiments was completely to revise the difference in longitude between Dublin and Armagh from 1 minute 14.220 seconds to 1 minute 14.258 seconds.  In other words, by letting off several pounds of high explosive into the night sky, Thomas Romney Robinson showed that Armagh was further west of Dublin than anyone had suspected by a distance of nearly 50 centimetres!

To find out more about Adam visit:

Thomas Romney Robinson

Robinson Anemometer

The young Robinson

Slieve Gullion

Armagh Observatory circa 1883

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