John Drake - Flint and Silver

But Stevenson set Treasure Island in the second half of the eighteenth century, as can be calculated from the principal date in the book: 20th July 1754, written by Billy Bones on the treasure map. My guess is that the map was at least five years old when Jim Hawkins found it, placing the action of Treasure Island in the 1760s. Probably Stevenson did this because his story was about the consequences of past piracy: buried treasure, long since lost.

A final word on the real captain England and those whom he exemplifies: he was regarded as a gentle pirate because he used torture only when necessary, other means of persuasion having failed. Most of the rest were not so kind, and all those persons who like horror – real horror – should study contemporary accounts of these pirates.

And so to the treasure itself…

Long John's estimate was that the treasure was worth about Ј800,000 in the mighty golden pounds of 1752, representing a truly enormous sum in the miserable paper pounds of the twenty-first century. It was worth all the more in the eighteenth century because then so much was bought on credit via written promises to pay; a system even worse than plastic cards in the slippery ease with which it led into debt and inability to pay. Thus ready gold or silver was warmly welcomed.

Turning to actual figures, Research Paper 99/20 of the House of Commons Library February 1999 calculates that prices rose by a factor of 118 between 1750 and 1998, which seems seriously too low a figure, reflecting the fact that politicians now, as in the eighteenth century, should never be trusted with money. But even that dubious figure would turn Silver's estimate into Ј94.4 million.

Substituting honesty for statistics, an able seaman RN was paid 24 shillings (Ј1.20) per month in the 1750s, while his modern equivalent, a trained rating, is paid Ј15,500 to Ј26,000 per year, say Ј20,000 on average, or roughly Ј1,666 a month – approximately 1,400 times inflation.

Similarly, a dockyard clerk, a middle-ranking, white-collar professional, earned Ј30-40 per year in the late eighteenth century, while an equivalent, middle-grade, modern administrator might reasonably expect something like Ј30,000- 40,000.

Factors such as tax and the relative cost of manufactured goods versus services have turned dizzy cartwheels over the past two hundred and fifty years, but we will not go far wrong in adding three noughts and assuming that, in modern money, the treasure was worth something like Ј800,000,000.

Which brings us up to date so far as the value goes. But how do we reckon the date?

On Friday, 15th October 1582, enlightened Catholic Europe adopted the new Gregorian calendar proposed by the Calabrian astronomer Aloysius Lilius, and decreed by His Holiness Pope Gregory XIII, after whom it is named.

This calendar corrected faults in the previous Julian calendar, which had caused natural events like the equinoxes (twice-yearly occasions when the day and night are of equal duration) to "drift backwards" through successive Julian years, occurring later and later as each year passed.

The change to the Gregorian Calendar required that Thursday, 4th October 1582 be followed by the newly reckoned Friday, 15th October.

Protestant Europe, including England and its overseas possessions, fiercely resisted anything Catholic – including the Gregorian Calendar – until the stupidity of this policy became too gross to be ignored.

Finally, grudgingly, one hundred and seventy years late, and with riots by the ignorant, howling:

"Give us back our eleven days!" the British adopted the Gregorian Calendar, with the result that Wednesday, 2nd September 1752 was followed by Thursday, 14th September.

Events described in this book – particularly the burying of the treasure – take place both before and after the switchover date. To avoid confusion, all dates are given in the Julian, or old-style reckoning.

This map, made in 1689 by Captain Santos Almeida of the Portuguese Navy, guided Captain Springer to the Island in 1749. It gives the Island's features their original names, and notes the compass variation. It also gives latitude and longitude plus sailing instructions to locate the Island: information later removed by someone else.

The map also gives several features bearing on future adventures of John Silver and Joe Flint – features integral to Pieces of Eight: the sequel to Flint and Silver.