Nine o'clock Oxford time

I had a room opposite Tom Tower in my second year. The bell rings 101 times at five past nine in the evening which was a nuisance at times! I understood that it was to summon the students back in for the night but I could never understand why five past nine. It turns out that it is a result of G.M.T. When the railways made a common time for the UK vital to keep trains running on time, the idea of using the Sun highest in the sky in that town as noon went out the window. Time was now fixed by noon at Greenwich. Noon at Greenwich is five minutes ahead of Oxford, so by ringing at five past nine G.M.T. the bell was still being rung at the true 9pm local time.