July 27 – Birth of Sir George Airy (1801)

Today is the birthday of Sir George Biddell Airy, born in 1801 at Alnwick (I think you pronounce it ‘annick’, but don’t quote me) in Northumberland, England.  If you pay a visit, you’ll probably recognise Alnwick from its castle, which has starred in two Harry Potter films, Downton Abbey, Star Trek: the Next Generation and The Black Adder.

Airy shone as a student at Cambridge, probably to the annoyance of his fellows. Like Isaac Newton before him, Airy was a sizar, a class of student whose parents could not afford to pay the full fees, but who were allowed entry on the understanding that they paid their way by working as a servant at the university while studying.

A mere six years after entering Cambridge Airy was appointed Lucasian professor of mathematics, one of the most prestigious academic posts anywhere, held over the years by (among others) Charles Babbage, Paul Dirac,  Stephen Hawking, and the aforementioned fellow sizar Isaac Newton.

Airy made several important discoveries in his time, including a tiny inequality in the motions of Venus and Earth that led to an overhaul of Delambre‘s solar tables.  He also came up with a new figure for the mean density of the Earth.  This was achieved by measuring the change in gravity as one descends into the Earth by using changes in the swing rate of a pendulum at the top and bottom of a deep coal mine. It turns out that at just over 1000 feet down the pendulum ‘gains’ two and a quarter seconds a day. From this, Airy was somehow able to calculate a specific density of about 6.5. Today it is thought to be 5.5.

Today’s picture is the un-astronomical A Shell Forge, by war artist Anna Airy, George’s granddaughter.

A Shell Forge (Anna Airy).
A Shell Forge (Anna Airy).

1879  –  Discovery of C-type asteroid 200 Dynamene by C H F Peters.