At Perth, the mails for Dundee and the northern Highlands are despatched, the latter being forwarded by a mail-train which runs on the Highland Railway _viâ_ Inverness. Again the Special Mail starts on its way, there being only one stop--at Forfar--before arriving at Aberdeen, where the journey ends. Here the last bags are despatched. The carriage is clear. The sorting-boxes are carefully searched, to see that no letters have been left in them; and the carriage is then taken charge of by the railway officials, to be thoroughly cleansed and made ready for the return journey on the following day. The duties on the way to London are performed in a precisely similar manner to those on the journey northwards. EARLY TELEGRAPHS. The ancient Greeks and Romans practised telegraphy with the help of pots filled with straw and twigs saturated in oil, which, being placed in rows, expressed certain letters according to the order in which they were lighted; but the only one of their contrivances that merits a detailed description was that invented by a Grecian general named Æneas, who flourished in the time of Aristotle, intended for communication between the generals of an army. It consisted of two exactly similar earthen vessels, filled with water, each provided with a cock that would discharge an equal quantity of water in a given time, so that the whole or any part of the contents would escape in precisely the same period from both vessels. On the surface of each floated a piece of cork supporting an upright, marked off into divisions, each division having a certain sentence inscribed upon it. One of the vessels was placed at each station; and when either party desired to communicate, he lighted a torch, which he held aloft until the other did the same, as a sign that he was all attention. On the sender of the message lowering or extinguishing his torch, each party immediately opened the cock of his vessel, and so left it until the sender relighted his torch, when it was at once closed. The receiver then read the sentence on the division of the upright that was level with the mouth of the vessel, and which, if everything had been executed with exactness, corresponded with that of the sender, and so conveyed the desired intimation. We must here pause a moment to point out one great advantage that this contrivance, simple as it undoubtedly was, will be seen to possess over the more scientific ones that follow, and that was, its equal efficacy in any sort of country and in any position, whether on a plain, on the summit of a hill, or in a sequestered valley.