Let us now try to show to how great an extent the Travelling Post-office has contributed to the acceleration of correspondence from place to place. On an examination of the letters received from Harrow, it is found that there are three for Aberdeen; and a similar number for that city will be received from the several towns between London and Rugby, and so on. Of course, the number of letters mentioned would not be sufficient for a direct bag between each of these places and Aberdeen; but the small numbers referred to being brought together in the Travelling Post-office, it is found that when the train arrives at Carlisle a sufficient amount of correspondence for the northern city has been received to fill a large bag. This bag is therefore closed at that point, and a fresh one hung up, to contain the correspondence for that city received northwards of Carlisle. The same may be said of the other large towns in Scotland. Now, if there were no Travelling Post-office, how would the few letters for Aberdeen emanating from the various towns in England be dealt with? In the first place, they would have to be picked up by a stopping train, and even if this train ran direct to Aberdeen, there would be a difference in the time of arrival of at least eight hours. But the letters could not go direct in such a case, as that would mean the making-up of separate bags at each place; and we have already shown that the letters are too few in number to justify such an arrangement. They would have to be collected at some central office, say at Birmingham, where they would of necessity be detained some time; so that altogether it is probable they would not arrive at their destination early enough to be delivered on the day following that of posting. What, however, is the case now? Thanks to the Travelling Post-office with its mail-bag apparatus, the letters are whirled along at close upon fifty miles an hour without intermission, thus admitting of the delivery of letters from London at so remote a place as Aberdeen long before noon on the following day. We will now assume that the train has arrived at Rugby--the distance eighty-four miles. At this station mails for Coventry, Birmingham, &c., are left to be forwarded by a branch train. After a stop of four minutes, the train again speeds on its way, the next stopping-place being Tamworth. Here a large number of mail-bags are despatched, including those for the Midland Travelling Post-office, going north to Newcastle-on-Tyne, which serves Derbyshire, Yorkshire, and the whole country-side bordering on the north-east coast; for the Shrewsbury mail-train, which serves the whole of Mid-Wales; and for the Lincoln mail-train, which serves Nottinghamshire and Lincolnshire.