The division of London into districts naturally induced inquiry as to the swiftest and cheapest means of conveyance over the comparatively short distances between office and office. Mail-carts were at once put in use, but I was inclined to hope that a swifter mode might be found--one, too, less liable to interruption. I called to mind an attempt made thirty or forty years before by a Mr. Vallance, to propel a vehicle containing passengers through a partially exhausted tube; the project then in view being the construction of an airtight tunnel between London and Brighton. Of this I had received some account from my friend, the late Mr. Moses Ricardo, who had been a passenger in a short experimental trip. He told me, indeed, that on reaching the terminus he and those with him "got a bang" by the abrupt stoppage of the vehicle, no arrangement having been made for its gradual check; but knowing that such arrangement was very feasible, and apprehending no severe consequences in any case to letters or newspapers, I hoped a similar plan might prove applicable to the purpose in hand. I therefore called in the assistance of two able engineers, viz., Mr. Charles Hutton Gregory, and Mr. Edward Alfred Cowper, who jointly made, with great care and skill, a full investigation into the practicability of the scheme. To avoid needless expense, they conducted their experiments on a small scale, nor was any line of tubes of a size for actual use ever laid down, though Mr. Cowper devised and constructed a very ingenious air-pump, especially applicable to the exhaustion of the tubes, as was attested by its complete success. The conclusion arrived at was that the plan was perfectly practicable, but that for distances so short the economy in time would not be sufficient to justify the additional expense involved in the innovation. Some years later, remembering this ground of condemnation, I inquired whether the plan could not be made available for a larger purpose. Up to that time it had not been found practicable to convey the mail from London to Dublin, Glasgow, Edinburgh, or Paris, within the compass of a night; acceleration, therefore, up to this point was highly desirable. Even now (1868), much as has been done, the work is not absolutely perfect; while the increased expense by which the last abridgement, though of not more than two or three hours, has been effected, exceeds £15,000 per annum. Now my hope was that by the establishment of tubular conveyance so far as Dover on the one hand, and Crewe on the other, the necessary acceleration in all the three services--Irish, Scotch, and French--might be obtained; and judging from the estimate made with reference to the London District, I hoped that the cost would not greatly exceed the actual payment for the railway service to be superseded. To these larger questions, therefore, the attention of Messrs. Gregory and Cowper was now turned.