为什么一位电影演员会在伦敦地铁里藏书呢？为了鼓励大众多读书，电影《哈利·波特》的女主角扮演者艾玛·沃森在伦敦地铁里藏了一百本书供众人去发现并浏览阅读。“地铁图书”（Books On The Underground）活动计划在英国首都伦敦的交通系统里放成千上万本书供乘客阅读。

Now here's what I call a turn-up for the books - a film star's been giving away free books on the London Underground. If you're a bookworm, a Harry Potter fan and a London Underground user then it's been an exciting month for you.

Emma Watson, who starred in films based on the novels about a fictional schoolboy wizard, has been hiding books on the Tube for passengers to leaf through.

It's part of the Books On The Underground movement, which has a simple aim: to get more people burying themselves in literature. And the way they do it is to leave tomes on trains for commuters to pick up, dip into and then leave for another lucky reader to skim.

The movement started out in 2012 and drops off about 150 volumes a week in stations across the UK's capital. Talking about Watson's participation in the project, the manager of Books On The Underground, Cordelia Oxley, said, "The reaction has been phenomenal. It must be a mixture of how much everyone adores Emma, and how exciting it is to find something as wonderful as a new book on your journey."

The 100 or so editions Watson left for passengers to pore over were even more special because she left a hand-written inscription. The paperbacks were copies of Kaya Angelou's Mom & Me & Mom.

One person who discovered a copy of the book on the Tube said she felt like the character Charlie Bucket – a boy who finds a golden ticket to the world's greatest chocolate factory – in the Roald Dahl classic, Charlie and the Chocolate Factory.

Watson became a UN Women Goodwill Ambassador in the summer of 2014 and has since started devouring as many books and essays on equality and feminism as possible. She has also started her own book club.

So, why not take a leaf out of Emma Watson's book and leave a copy of your favourite book on a train? It could make a stranger's life richer.