Following the British Calendar Act of 1751, Britain adopted the Gregorian Calendar in 1752. However, the current Julian calendar system required them to drop eleven days in order to sync themselves with the proposed Gregorian Calendar. So, on the evening of 2nd September 1752, the population of Britain and its American colonies went to sleep and awoke the next morning to 14th September 1752.
The changeover is also responsible for New Year’s Day being celebrated on 1st January, as before then it had been celebrated on 26th March.
As a result of Calendar Adjustment Day, there was rioting on the streets by those who felt cheated, and demanded the eleven days back!