Eighteenth Book
I/lustration 341
well coated with pítch, and íron rings put on from top to bottom. When thís machine is fíníshed, it should be erected so as to make a tríangle of the form A. Bis the second method of a screw or snail. allustration 341) In the screw B as well, I díd not want to demonstrate more than one tum of the screw-threads that rnake the channels, so as not to confuse the judgement or the understandíng. In the screw rnarked A, it is illustrated how you make squares all along the wood: then begin at one comer and cut all the squares diagonally across right to the end; and in thís way you will achíeve what you desire. If it seems dífficult to lay the boards on the screw A, take cow's leather well-tallowed, and lay it over that. To get out the congealed mud frorn inside the enclosure where the pier is to be built. The instrument which I shall illustrate here is quite wonderful for that purpose. It fills and empties by ítself, and works like a purse. A shows it closed, B from the open interior; C open from the outside. The instrument is provided with iron plates, [!fol. 365v] (Illustration 342) which have play at the edges of the small square in the centre; and each square has a ring or collar to suspend it from rapes. In the srnall centre square there is a large ring, with a very thick rope fastened to it, which raises and lowers it. And in the four there are to be four pieces, which are fastened to one rope. In lowering this instrument, care should be taken to hold the rope that has the four pieces of rope fastened to it, so that when it is pulled only the rope in Illustration 342
[517]
fUNDACIÓl\' Jt:A;..¡ELO TURRIAJ\0