There is no doubt, however, that the success of the Travelling Post Office was the first revelation to the railway companies, and to the public, of what could be done on a train while in motion, but much was needed in the direction of improving the permanent way and the springs and general make-up of the rolling stock before any further advances could take place. Perhaps on this ground alone we can spare a little sympathy for the Post Office servants, who during the long years when railway travelling was neither smooth nor comfortable, had to keep their heads and their feet while the train raced across country. The first permanent sorting carriage was built by the Grand Junction Railway Company, and this carriage was fitted with an apparatus for exchanging mail bags _en route_. The appliance consisted of an iron frame covered with netting, and was fixed to the near side of the carriage. It was made to open out for the purpose of receiving a bag suspended from the arm of a standard erected beside the railway line. Simultaneously with the delivery of a bag into the carriage net, a bag was dropped on to the bare ground by another mechanical contrivance, guard boards being fixed by the side of the permanent way to prevent the bag from getting under the wheels of the carriage. This apparatus was first tried in 1838 on the London and Birmingham Railway at Boxmoor. On the 17th September 1838, the London and Birmingham Railway was opened throughout its entire length, and the Travelling Post Office was permanently established on that line. Two mails were despatched from Euston daily, the first a day mail at 11 A.M. and the night mail at 8.30 P.M. The immediate effect of the introduction of the Travelling Post Office was to render unnecessary the making up of some 800 or 900 bags. Each town now made up one bag for the train, instead of the fourteen or fifteen which had to be made up for the mail coach, and the Travelling Post Office re-sorted the letters and made up bags for the various towns which it served. In the year 1843 the number of bags made up in the London and Preston Travelling Post Office down mail was 51 and in the up mail 44. The number of bags at present made up in the same Travelling Post Office, which now runs from London to Aberdeen, is nearly 400 on the down journey and about 300 on the up journey. In 1910 there were in Great Britain no less than 73 separate Travelling Post Offices, composed of 150 specially constructed carriages. In 1848 the apparatus for exchanging letters was considerably altered and simplified. For the first time nets were fixed by the side of the permanent way in which were caught the bags delivered from the Travelling Post Office, and a new variety of winged carriage net was provided with detaching lines, which were used to grip and detach the pouch from the arm in which it was held. Many alterations have since been made in the working of this apparatus, but the principle of the thing remains the same.