Happy 150th anniversary of the London Underground! According to Transport for London , today marks 150 years since the first underground journey took place between Paddington and Farringdon on the Metropolitan Railway.
Except the anniversary hasn't always been celebrated as the 9th. As Diamond Geezer  points out, The London Transport museum still records  the first section as opening on the 10th; and the Manchester Guardian of 11th January 1863 agrees, referring  to the "the Metropolitan (underground) Railway" being opened "yesterday".
What gives? The answer could be seen as a rather sad sign of the times. The 9th and 10th are both anniversaries: the latter of the day the railway opened to the public; the former of the day a private journey was arranged for the directors , ending with a banquet for 600 dignitaries on the platform of Farringdon station. We used to celebrate the date of a wondrous new transport system being opened to the world. Now we celebrate a corporate dinner.