"In default of getting it, will go back to course of practice (at Bar) I must and will follow, not for my necessity of estate but for my credit's sake, which I fear by being out of action will wear." His brother Anthony spent the best part of his life abroad, presumably on some secret missions; and as Francis was the recipient of his letters it was doubtless that "folded writing" which so puzzled their mother which was used for the safety and secrecy of their correspondence. Indeed to what a fine point the biliteral method must have been brought by Bacon and his correspondents is shown by the extraordinarily minute differences given in his own setting forth of the symbols for "a" and "b" etc., in the "_De Augmentis_" of 1623 and later. In the edition printed in Latin in Paris the next year, 1624, by Peter Mettayer, the differences, possibly through some imperfection of printing, are so minute that even the reader studying the characters set before him, with the extra elucidation of their being placed under their proper headings, finds it almost impossible to understand them. The cutting for instance of the "n" which represents "a" and that which represents "b" seems, even after prolonged study, to be the same. It is to be noticed that Bacon in setting forth the cipher in its completeness directs attention to its infinite possibilities and variations. The organised repetition of any two symbols in combinations of not more than five for one or both symbols may convey ideas. Not letters only but colours, bells, cannon, or other sounds may be used with effect. All the senses may be employed, or any or some of them, in endless combinations. Again it is to be noted that even in his first allusion to the system in 1605, he says, "to write Omnia per Omnia, which is undoubtedly possible, with a proportion _Quintuple at most_, of the writing infoulding, to the writing infoulded." "Quintuple at most!" But in the instances of his system which he gives eighteen years later, when probably his time for secret writing as a matter of business had ceased, and when from the lofty altitude of the Woolsack he could behold unmoved any who had concealments to make--provided of course that they were not connected with bribes--there is only one method given, that of five infolding letters for each one infolded. In the later and fuller period he speaks also of the one necessary condition "that the infoulding writing shall contain _at least five times as many letters_ as the writing infoulded"-- Even in the example which he gives "Do not go till I come," there is a superfluous letter,--the final "e;" as though he wished to mislead the reader by inference as well as by direct statement.