Travellers who are in the habit of journeying over the principal railway lines, must at some time or other have noticed certain carriages in the express trains which had an unusually dull and van-like appearance, though set off with a gilded crown and the well-known letters V.R., and that generally these carriages appeared to have no proper doors, and were possessed of none but very diminutive windows--on one side, at any rate. It will have been observed, also, that sometimes two, three, or more of such carriages are placed end to end in certain trains, and that a hooded gangway or passage enables those inside one carriage to visit any or all of the other carriages. When the small square holes or dwarf doorways which communicate with the outside are open, a glare of light is seen within, which reveals a variety of human legs and much canvas--the latter in the shape of mail-bags, either suspended from the walls of the carriage or lying on the floor. These carriages are what are called in the Post-office the "Travelling Post-office"; or, when brevity is desirable--as is often the case--the "T.P.O." There are several travelling post-offices of more or less importance pursuing their rapid flight during the night in different quarters of the country; but the most important, no doubt, are the "London and North-Western and Caledonian," running from London to Aberdeen; the "Midland," running from Newcastle diagonally across England to Bristol; and the "London and Holyhead" travelling post-office, by which the Irish mails to Dublin are conveyed as far as Holyhead. [Illustration: Travelling Post-office.]