And now, unless we at once return from our digression, we shall not be in time to see the great night-mail despatched from St. Martin's-le-Grand. Whilst we have been occupied with a contemplation of the few waifs and strays of our national correspondence, the great bulk of that correspondence has been well and carefully disposed of: the letters and newspapers which we saw two hours ago as a mass of inextricable confusion, are now carefully stowed away in their respective bags, and not a letter or newspaper can be found. The hall clock is silently approaching the hour of eight, when the bags must all be sealed and ready to leave the place. At five minutes before that time, all is still bustle and activity; five minutes perhaps after that hour the establishment is nearly deserted. "Everything is done on military principles to minute time." "The drill and subdivisions of duties are so perfect," adds a close observer, "that the alternations are high pressure and sudden collapse." This is the more remarkable, inasmuch as the Post-Office, is subject to great variations in the amount of work to be done. Particular nights in the week, Mondays and Tuesdays for example, are known as the "heaviest," and even such events as elections, influence the labour to be performed within the same given time. During the last election for Lambeth, 40,000 circulars were posted in London in one day, and properly disposed of. On the 14th of February last, 957,000 extra letters, or valentines, passed through the Circulation Office in London. Compared with Valentine's Day 1863, there was an increase of a quarter of a million letters! In place of the old mail-coaches waiting in the yard of the office until the work is completed inside, we have now the well-known mail-vans. As they are rapidly supplied with bags, they chase each other to the various railway stations, from which, to all points of the compass, the night-mails now depart. Half an hour afterwards, we find ourselves in one of these trains watching operations not dissimilar to those we have just left, but much more wonderful, considering how they are accomplished. THE TRAVELLING POST-OFFICE.