Other malpractices were less easy of detection. All the claims, before they were passed, came under Allen's personal inspection; and to determine whether these were fraudulent or not needed no special aptitude. But whether at some distant part of the country two or more postmasters were in collusion, or whether without collusion they were bringing to account less postage than they collected, were questions the solution of which demanded qualifications of a different order. As the result of reflection or observation, or more probably of both combined, Allen laid down for his own guidance certain propositions as simple as they were no doubt sound. Of these one was that the correspondence passing between two given places, far from being liable to violent fluctuations, might be relied on to maintain a nearly uniform level. It is certain that in our own days, when locomotion is easy and the movements of large parts of the population are influenced by the weather and other considerations, the principle which this proposition embodies would not hold good; but in the earlier half of the eighteenth century Allen regarded it, and probably not without reason, as a safe guide. When, therefore, the correspondence passing between two places during a certain period had once been ascertained, he adopted this as a standard, and any variation of the amount immediately excited his suspicions. "At Christchurch and Ringwood," he writes, "fully inform yourself why the letters which formerly were sent between those places and Salisbury are now almost entirely sunk." At York, during the quarter ending Midsummer 1734, the postage on bye-letters amounted to £165, as against £176 during the corresponding quarter of the previous year. This he affirms must proceed, not from "deadness in trade," but from "some mismanagement in the office." Between Appleby and Brough the letters passing in December were fifteen, whereas in the two preceding months they had been only three. "Let me know at once," he writes, "the cause of the difference." Another proposition which Allen established as a rule of conduct was that between two trading towns in the same neighbourhood there must almost of necessity be correspondence. He noticed with surprise that between Stone and Coventry, according to the vouchers sent him, not a single letter had passed during a whole quarter. "I will not say it is impossible," he writes to the surveyor, "that no letters should during this time pass between such trading places, but during your stay at Stone I must in a particular manner desire you will examine whether you receive none."