Some novel data on tides

Reading New Scientist (NS) edition 2556 dated 17 June 2006, I found an historical article on William Hutchinson (WH).  He was obviously a very bright lad and became an 18th century mariner who led an interesting and productive life.  On one of his voyages he found a method of reducing scurvy that the Chinese used.  Most people know that lime juice was discovered later, and was a much more effective cure than the one that WH found.  The British Navy and the Brits themselves now have the appellation; 'Limey' as a result of this second discovery.

WH noted that the Chinese used brewed tea as a relief against that dreaded disease.

WH also became a privateer.  At that point NS defined what a privateer was.  He was a pirate of a very special type.  Not one of the run-of-the-mill thieves, but a pirate licensed by The Admiralty to attack and rob enemy vessels.  This enabled the art of thievery to be legitimised by the strongest nation (at that time) on the planet.  At the privateering time of his life he joined forces with Captain Fortunatus Wright.  Later WH commanded his own ship.

But WH made his most valuable contribution to science after he retired.  He remembered one particular incident when the large part of a vessel was ripped off as it crossed a bar going into harbour.  The naval world required a reliable way of judging tidal heights.  So in 1764 when he was finally ashore and retired in a house close to the Old Dock at Liverpool, he set about making twice daily measurements of the sea level against a set of marks cut into the masonry at the side of the harbour.  He not only recorded the water height, but the time, the wind strength and its direction,  And what I would not have expected at that date, he also recorded the barometric air pressure and general weather conditions.

Hutchinson's diligence quickly paid off as his first four years of recordings played a vital part in producing Britain's first accurate set of tide tables in 1767.  He handed the first 300 entries in his journal to a local mathematician Richard Holden and his brother George.  The two men were working on a new way to predict tides and they used WH's data to check its accuracy.  In 1770 they published tide tables for Liverpool that were so good that all Liverpool pilots were required to use them, or face a £5 fine (no small sum in those days).  Unfortunately, the Holdens didn't return the pages of data and they are now lost.  But WH's remaining pages that stretched from the beginning of 1768 to 10th August 1793 were retained.  The man finally retired soon after that date.

One of the snippets of data that the NS article recorded is that for every millibar of increasing air pressure, the sea level is depress by a centimetre.  Across what range of values and geographic positions that rule applies; the article did not say.

Research on tides and tide-prediction have all benefited hugely by the diligent work of William Hutchinson.  Recently the data has been used to investigate a subject that would never have entered the head of that eighteenth century mariner; that of Global Warming.  Woodworth and his colleagues at the Proudman Laboratory (http://www.pol.ac.uk/) have compiled one of the world's longest near-continuous records of tidal height.  The first 25 years 7 months and 10 days belong to Hutchinson.  This record provides proof that sea levels have been rising since the 18th century, and that these rises have accelerated during the second half of the 19th century.  This is exactly in line with the known increase in the production of greenhouse gases

Accuracy of WH's records have been questioned as a result of boredom and creeping old age of the man.  Woodworth disputes this slur on his hero.  WH's records of air pressure have shot down the libels that some of the records were probably made up when he was too tired, or the weather was too foul to record the true figures.  At that early date the association between sea-level and barometric pressure was not known, but recent checks have shown that the variations in the two sets of data correlate very closely.  It is argued that this correlation proves the rigour of William Hutchinson, even into his old age.

At this point I will deviate from the NS story and add my own comments.  There is now a mathematical technique that allows investigators to verify the truth of sets of records made by a recorder.  New Scientist published an article a year or so back on how the Inland Revenue verify (or otherwise) the truth of a list of data compiled by, for example, a shopkeeper; when he uses it as evidence of monies collected.  No details were given as to the actual maths method, but I know of another instance where this technique was used:

The International Nuclear Inspectorate (INI) examined  sets of data drawn up by BNFL at one of their plants.  The INI found that the data had been artificially hatched.  I won't go into the much longer story that culminated with a lot of senior heads rolling at BNFL.  So beware, TRUTH is a very fine fluid that seeps out of all manner of unexpected places.  Not only do liars need excellent memories, but they also need a high level of mathematical knowledge.