Few of the difficulties we experience in investigating the meaning of these three chapters were felt by the correspondent to whom the Friar addressed them as letters. He and Bacon had long been in communication with each other, and as both knew the substance which formed the _real_ subject of these letters, Bacon was at liberty to call it chalk or cheese or what he willed. They appear to have had some system of numerical signs, the meaning of which is lost to us. The tenth chapter begins with a reference to a letter received by Bacon from his correspondent in the year 602 A.H., and as the date is given in words, not figures, it can hardly have been mistaken by the scribes. Now the year 602 A.H. began on 18th Aug., 1205 A.D., nine years before Bacon was born. The number 602, therefore, is either a blind, or a conventional sign or key. The same may be said of the number 630 in the first line of Chap. XI., and of the totally unnecessary 30 which occurs just before the anagram in the same chapter—“(_sit_) pondus totum 30,” _i.e._ let the total weight be 30. No one can have ever wanted to know the total weight of the mixture in question: every one wanted to know the proportions of the ingredients. Our ignorance of these signs creates difficulties for us which did not exist for the initiated in Bacon’s time. As will be shown hereafter, Bacon has occasionally availed himself in Chaps. IX., X., and XI. of Nos. 2 and 4 of the cryptic methods he has given us; but these methods apply only to words and phrases, and the wily Franciscan did not think it necessary to allude to the more general method by which he set forth so much of his statement as is contained in Chaps. IX. and X. We cannot discuss cryptograms here: suffice it to say that some of the early methods were too tedious and some too complicated to be employed throughout the whole length of Chaps. IX. and X. The method he appears to have adopted (as the result will show) was that known long afterwards as the “Argyle cipher,” of which the following letter from Thackeray’s “Esmond” is an example. The real contents of this letter are the phrases within brackets:— “[_The King will take_] medicine on Thursday. His Majesty is better than he hath been of late, though incommoded by indigestion from his too great appetite. Madame Maintenon continues well. They have performed a play of Mons. Racine at St. Cyr.... [_The Viscount Castlewood’s passports_] were refused to him, ’twas said; his lordship being sued by a goldsmith for _Vaisselle plate_ and a pearl necklace supplied to Mademoiselle Meruel of the French Comedy. ’Tis a pity such news should get abroad [_and travel to England_] about our young nobility here. Mademoiselle Meruel has been sent to Fort l’Evesque; they say she ordered not only plate, but furniture, and a carriage and horses [_under that lords name_], of which extravagance his unfortunate Viscountess knows nothing.