La plus belle plume

At the TLS, Matthew Cobb considers the life and work of the French naturalist Buffon:

Buffon’s first passion was mathematics, and in 1733 he solved a major problem in probability and geometry, now known as “Buffon’s needle”. This involves calculating the probability that a needle, dropped on to a surface covered with parallel lines, will cross two lines, and requires an estimation of the value of pi. Buffon’s interest in this problem was prompted by trying to work out the odds of winning at a popular gambling game. Given his subsequent conversion to natural history, he would no doubt have been pleased to learn that in the ant Leptothorax albipennis, the workers appear to use a variant of his solution to estimate the size of potential nest-sites by measuring the frequency with which they cross pheromone trails they have laid.

Buffon’s continuing interest in numbers is shown in some fascinating, but depressing, pages of L’Histoire naturelle where he tallied the ages at which people died in and around Paris, and calculated life expectancies. Most children who reached the age of twelve could expect to live until their late thirties, while most of those who made it to fifty could hope to live another sixteen years and seven months. Resolutely cheerful, Buffon claimed that we only start to live morally when we can order our thoughts, and that therefore the first fifteen years of our existence should be discounted. As a result, a twenty-five-year-old would have lived only a quarter of their life, even though they could expect to die aged fifty-six.