From Jay Pasachoff, Hopkins Observatory, Williams College
For years, I have been describing plate tectonics to my classes by saying that the continents drift apart at about the rate at which fingernails grow – roughly a millimetre a week. Following David Jackson’s letter that described his observations of his own fingernail growth (21 January, p 21) and the earlier article on William Bean’s fingernail growth (24/31 December, p 37), I can’t resist pointing out this fact to your readership too.
Williamstown, Massachusetts, US
