Now and Venn - Frank McNally on famous cryptographers, Venn diagrams, and equestrian dramatics

Born 500 years ago on April 5th, Frenchman Blaise de Vigenère (1523-1596) is now best remembered as a cryptographer, credited with the “Vigenère Cipher”, a code that remained unbroken for centuries. But as a traveller in Italy, he also once witnessed Michelangelo at work and left a vivid description, in plain language: “He had passed his 60th year, and although he was not very strong, yet in a quarter of an hour he caused more splinters to fall from a very hard block of marble than three young masons in three or four times as long . . . he attacked the work with such energy and fire that I thought it would fly into pieces. With one blow he brought down fragments three or four fingers in breadth, and so exactly at the point marked, that if only a little more marble had fallen he would have risked spoiling the whole work.”

I said above that Vigenère was “credited” with the cipher named for him. The qualification is necessary because, confusingly, he didn’t invent it.

He was so successful at publicising one devised by the Italian Giovan Battista Bellaso that it eventually became associated with Vigenère instead, although in fairness to the Frenchman, he did go on to create a better version. A contemporary who could have benefitted from his expertise was Mary Queen of Scots, whose 1586 letter approving the plot to assassinate her cousin Queen Elizabeth, was also encrypted, but not well enough. When that was decoded, she was decapitated.

The Vigenère Cipher was only cracked in the 1850s. And among its would-be successors in unbreakability was a system invented by a Dubliner, John Francis Byrne (1880-1960). Like previous attempts, his used parallel alphabets, but with an algorithm that, when substituting one letter for another, became “chaotic”. Hence his name for it: the Chaocipher.

General selection – Frank McNally on national stereotypes, Greek (and table quiz) heroes, and a stamp of greatness

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Blood brothers – Frank McNally on the deaths of two young men, one Irish, in the Korean War

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Hard Border – Frank McNally on a visit to the Korean Demilitarised Zone

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Transmigration of Seoul – Frank McNally on a long-awaited trip to South Korea

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After emigrating to the US, he tried and failed to sell it to the state department and other potential customers. In the end, it won him neither the fortune he had hoped for, nor the Nobel prize a relative had predicted. But a $5,000 prize offered in his memoir to anyone who could crack a two-line sample was never successfully claimed.

Like Giovan Battista Bellaso, Byrne has earned a second-hand fame. He is best known today as a friend of James Joyce, once hosted for the night at Byrne’s home, No 7 Eccles Street. The address was later transformed, by literary encryption, into the residence of Leopold Bloom.

Another of this week’s anniversaries is the centenary of the death of John Venn (1834-1923), Anglican clergyman and mathematician, immortalised by the much-loved diagrams he used for illustrating the relationships between different data sets. Apart from the eponym, Venn’s innovation has inspired at least two graphic memorials. At the Cambridge college of which he was president, a stained-glass window in his honour comprises three circles – yellow, blue, and purple – overlapping.

Less reverently, in his native Hull, a dual blue plaque recalls that along with his main claims to fame, Venn had a large beard. “Mathematician, philosopher & Anglican priest” reads the circle on the left; “Really strong beard game” reads the right; “John Venn” straddles the intersection.

Having lived until 1923, Venn might have foreseen one now-popular use for his diagrams in this part of the world.

The simplest way to introduce an uninitiated tourist to the complex political geography of “these islands” is via a series of overlapping circles, representing Ireland-the-country, Ireland-the-state, Ulster, Northern Ireland, Great Britain, and the UK. That Venn diagram is already complicated. It may get even more so soon.

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The plot of Glass Mask Theatre’s wittily-named Horse Play, which I saw at the weekend, has echoes of Shergar, kidnapped 40 years ago and never seen since.

But it’s mainly about the relationship between a jockey and his horse, brilliantly imagined by playwright Eva O’Connor and featuring a comically moving performance as the horse by Jarlath Tivnan, who for equine authenticity gives Jenny the Donkey a run for her money.

One small quibble. Before the play’s denouement, we are told that the horse’s disappearance may have related to its value at stud. But we are also told he was a winner for many years at “Cheltenham”.

These two sets of data don’t quite match. Flat racing champions may indeed go on to stud after their short, highly-strung careers. That male jumping horses can compete for much longer is partly down to a certain surgical procedure, which tends to have a calming effect. In a Venn diagram, the circles of “serial champion at Cheltenham” and “stud horse” would not usually intersect.

It’s a terrific play, at a lovely new venue, the Bestseller Café on Dublin’s Dawson Street. The bad news, if you haven’t seen it, is that the horse has bolted for now. The run ended on Saturday. But it deserves another, longer gallop somewhere. To adapt the metaphor, maybe somebody should open the Gate for it.