A number of light brass tubes, each having a socket to receive the end of the preceding joint, may be raised to any given height, and with the assistance of small loops of cord will fully answer the purpose here described. It will be necessary to have a small stud at one end of each joint, with a narrow slit at the end of the following tube to receive it, which being carried on in a right angle for about twice its width, will on being turned round serve as a key to prevent the joints separating. No. LI. A rule of gradation, which, with ease and method, reduceth all things to a private correspondence, most useful for secret intelligence. NOTE. _Vide_ Article V. No. LII. How to signify words, and a perfect discourse, by jangling of bells of any parish church, or by any musical instrument within hearing, in a seeming way of tuning it, or of an unskilful beginner. NOTE. By varying the order of arrangement, the whole alphabet may readily be rung on three bells; and these, being formed into sentences by short pauses between each word, will fully serve for distant conversation. For musical instruments, it is merely changing keys for bells, and the same purpose may be answered without the trouble of forming changes upon so small a number of fixed tones. A table is subjoined, by the use of which a combination of three bells is made to express the whole alphabet: A represented by 111 B 112 C 113 D 121 E 122 F 123 G 131 H 132 I 133 K 211 L 212 M 213 N 221 O 222 P 223 Q 231 R 232 S 233 T 311 V 312 U 313 W 321 X 322 Y 323 Z 333 No. LIII. A way how to make hollow and cover a water-screw, as big and as long as one pleaseth, in an easy and cheap way. NOTE. A leathern water-pipe, such as is used by the firemen, being nailed in a spiral form round a long circular pole, is the cheapest and most simple method yet discovered of making the Archimedean screw. No. LIV. How to make a water-screw tight, 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. NOTE. This may be readily effected either by making a coarse screw in the usual manner, and covering it with horn, or by fitting a spiral tube of glass on a wooden cylinder, and filling up the interstices with wax or any hard cement so as to project beyond the glass tube: this appears the most eligible method, though the former is the most economical.