[_A Rule of Gradation._] Probably some scheme which appeared to be capable of indefinite multiplication, the object of the secret correspondent always being to elude the utmost skill of an expert decipherer. Twenty-six lines of 26 letters of the alphabet each, would form a square; and supposing the letters placed in different order on each line, we might produce 26 linear alphabets, and 26 columnar alphabets; or change these by diagonal or other lines. These, and similar variations appear interminable, but it is questionable whether they would not delay rather than defy detection. 52. How to signifie words and a perfect Discourse by[5] jangling of[6] Bells of any Parish-Church, or by any Musical Instrument within hearing, in a seeming way of tuning it; or of an unskilful beginner. Footnotes [5] by the. [6] of the. [_A mysticall jangling of Bells._] There occurs at page 185, of Van Etten’s Math. Recreat. 1653, among the several heads of Problem 84, “Of changes in Bells.” He inquires: “Is it not an admirable thing to consider how the skill of numbers doth easily furnish us with the knowledge of mysterious hidden things?” He says: “It is often debated--what number of changes there might be made in 5, 6, 7, 8, or more bells;” observing thereon, “that a childe which can but multiply one number by another, may easily resolve it.” Not only have we here a kindred subject discussed, but also in language very analogous to that employed by the Marquis, particularly in the use of the words “mysterious,” “admirable,” and “a child;” the latter being a favourite similitude. 53. A way how to make hollow and cover a Water-scrue as big and as long as one pleaseth in an easie and cheap way. [_An hollowing of a Water-scrue._] This was probably no more than an ingenious piece of carpentry, to obtain an object which was then most likely of considerable importance. Three of his inventions refer to the Archimedian screw, so that the Marquis seems to have given the subject more than ordinary attention. 54. How to make a Water-scrue tite, and yet transparent, and free from breaking; but so clear, that one may palpably see the water or any heavy thing how and why it is mounted by turning. [_A transparent Water-scrue._] This invention does not appear to be offered as one of any other use than for pleasure and instruction, to “see the water or any heavy thing, how and why it mounteth by turning.” Was it not by such models that he had early informed his own mind? If the transparent covering was not to be glass or horn, the Marquis may have used the material proposed by Sir Hugh Plat in his “Jewel House of Art and Nature,” 1653, in which is given, at page 72, a recipe: “To make parchment clear and transparent to serve for divers purposes. This I commend, (he says) before oiled paper, because it is more lasting”--when employed for windows. 55.