My next attempt was to arrive at some rule which might serve for general guidance in such cases; and I came to the conclusion that, with some allowance for exceptions, the best test would be found by examining each tax “as to whether its productiveness has kept pace with the increasing number and prosperity of the nation. And the tax which proves most defective under this test is in all probability the one we are now in quest of.”[99] This test brought the tax I had in mind, viz., that on the transmission of letters, into bad pre-eminence; since, during the previous twenty years, viz., from 1815 to 1835 (my investigations being made in 1836), the absolute revenue derived from the Post Office, whether gross or net, instead of increasing, had even somewhat diminished; whereas, if it had merely kept pace with the growth of population, to say nothing of the concurrent spread of education, extension of trade, and advancement in prosperity, the revenue—I mean the net revenue—would have increased by no less than £500,000.[100] To try the matter further, I looked out for some other tax, which, while less exorbitant, was in other respects liable to as nearly as possible the same influences, and I naturally took the duty on stage-coaches. I found that the amount yielded by this, instead of diminishing, like that in question, had more than doubled in the same period; increasing from less than £218,000 to nearly £500,000, or about one hundred and twenty-eight per cent. I found, again, that if the Post Office revenue had risen in like proportion (and it seemed scarcely to be doubted that the demand for the conveyance of letters had increased in the same ratio as that for the conveyance of persons and parcels), the increase of net revenue would have been no less than £2,000,000.[101] The general fairness of this conclusion was afterwards shown by the fact; 116 per cent. having been the ratio of increase in the net revenue of the Post Office during the twenty years between 1847 and 1867. For yet further comparison, I turned to the accounts of the Post Office revenue in France, where the rates of postage were less exorbitant than with us, and taking the gross revenue (the net revenue not being given), I found that this had risen from somewhat less than £1,000,000 in 1821 to nearly £1,500,000 in 1835, about fifty-four per cent. in fourteen years.[102] Nor was I proceeding without authority in thus condemning the existing postal rates as unsound in policy, Sir Henry Parnell having attributed the non-increase of the revenue to the high duty charged on letters; while Mr. McCulloch had not only taken the same general view, but attributed the loss to the illicit conveyance of letters, for which the increased number of coaches gave so much facility.[103] Of the important services of Mr. Wallace in elucidating the same point I shall speak hereafter.