Attention had already been directed to this fact by Sir Henry Parnell.[70] Between the years 1815 and 1835 the duty on stage-coaches had increased from £218,000 to nearly £500,000 a year. During the same period the revenue of the Post Office, both gross and net, had not increased at all--in point of fact, it had slightly decreased. If it had kept pace with the increase of population, the annual net revenue would have increased by half a million. If it had increased in the same proportion as the duty on stage-coaches, the revenue of 1835 would have exceeded that of 1815 by no less than £2,000,000. These facts convinced Sir Rowland Hill that a reduction of the rates of postage was urgently necessary; and apart from financial considerations, the moral and intellectual results which would follow a facilitation of intercourse appealed powerfully to a reforming Radical.[71] Having arrived at the conviction that the Post Office offered most scope for his zeal, he found no lack of material to work upon. A Commission of Inquiry into the Revenue Departments had reported on the Post Office in 1829. A Commission of Inquiry on the Post Office had been sitting for some years, and had made numerous voluminous reports. Sir Rowland Hill set to work to make a careful study of the information contained in these reports, and as the result of this study evolved a complete plan for the reform and reorganization of the whole Post Office system, a plan involving the transformation both of the theory of Post Office finance, and of the methods of practical working.[72] His inquiries led him to examine the cost of the Post Office service as a whole, and its relation to the work performed by the Post Office in respect of individual letters, or, as he termed it, "the natural cost of conveying a letter."[73] The investigations and calculations made in this connection elucidated a fact of first importance, viz. that the cost of the conveyance of a letter from one town to another was exceedingly small, being on the average no more than nine-hundredths of a penny--in the case of a mail from London to Edinburgh the cost of conveyance was no more than one-thirty-sixth of a penny. This fact was developed. It was shown that not only was the cost for conveyance for the average of distance exceedingly small, but that it did not vary with the distance. The variation was rather in the inverse proportion to the number of letters enclosed in a mail.[74] Thus, while the average cost of the conveyance of a letter from London to Edinburgh was one-thirty-sixth of a penny, the cost of the conveyance of a letter for a shorter distance was often greater, owing to the small number of letters included in the mail. On these facts rests the whole case for uniformity of rate irrespective of distance:[75] and they are sufficient to demonstrate that the principle is fundamentally sound.