‘Must we document everything?’ exclaims Greta Gerwig, heroine of Noah Baumbach’s recent film Mistress America, when someone takes a casual snap of her on a mobile phone. Tweets, emails and instant photography allow us to keep constant track of our lives and to bombard the outside world with the details. But one wonders what effect 21st-century social media is having on the production of the conventional diary. Will such records eventually go the way of the handwritten letter?

Only time will tell, though it’s difficult to believe that many diarists of the future will possess the stamina and application of Jean Lucey Pratt. A suburban middle-class woman from Wembley in Middlesex, Pratt began writing a journal as a schoolgirl of fifteen in April 1925. She was still keeping