The date at which apertures on the outside of Post Offices were first introduced is unknown to us even approximately. All we can do is to fix two distant dates at one of which the contrivance existed, and at the other it existed not. On the 3rd of November 1712 Oxford, the Lord Treasurer, received an anonymous letter, and, being anxious to discover the writer, he invoked the assistance of the postmasters-general with a view to ascertain where and by whom it had been posted. Any such inquiry at the present time would be absolutely futile. One hundred and eighty years ago the postmasters-general, after an interval of twenty-four hours, were able to reply not only that the letter had been posted "at the receiving office of Mrs. Sandys, a threadshop two doors within Blackfryars Gateway," but that it had been posted "by a youth of about seventeen years old, in a whitish suit of cloathes, who was without a hat." It is difficult to believe that apertures can have existed then, and that the letter was not posted inside the office. That in 1757 the contrivance had come into existence, though possibly in a rude form, is beyond question. In that year an unfortunate woman was put on her trial for stealing a letter, and the sender was called upon to prove the posting. "On Tuesday the 7th of December 1756," he said, "I put this letter into the Post Office at the house of Mrs. Jeffreys at Bloomsbury, at about nine o'clock at night.... There is a window and a slip to put it into a little box from out of the street. I was not in the house. It is a very narrow box, and I was afraid my letter was gone down to the ground.[51] I asked Mrs. Jeffreys if my letter was safe after I had dropped it into the slip. She said your letter is safe and gone into the box." If the value of a contrivance depended upon the amount of ingenuity displayed in devising it, these apertures would be hardly deserving of mention; but in view of the convenience they afford, this short notice of them may not perhaps be considered out of place. [51] The box into which the letters fell was at this time an open one, _i.e._ without a cover and movable. It was not until 1792 that the letter-box was closed, fixed, and locked.