M. A. Rochon has likewise proposed a most ingenious substitute for the use of horn in the construction of the Archimedean screw, and other hydraulic instruments. It is formed (like the safety lamp of Sir H. Davy) of a coarse wire gauze which, on being immersed in pure fish-glue or size, forms when varnished a cheap and durable substitute for the use of glass. No. LV. A double water-screw, the innermost to mount the water, and the outermost for it to descend more in number of threads, and consequently in quantity of water, though much shorter than the innermost screw, by which the water ascendeth, a most extraordinary help for the turning of the screw to make the water rise. NOTE. This appears one of those extraordinary slight of hand discoveries in which the noble author is too apt to indulge; and though we may readily admit that two water-screws may be most advantageously employed in turning of any water-wheel, where an abundant supply is found at the top of the machine, it yet requires a greater share of penetration than we choose to take credit for, to discover how a larger quantity of water can descend than has been previously raised, or, if so, how the machine could be at all applied to the _raising_ of water. No. LVI. To provide and make, that all the weights of the descending side of a wheel shall be perpetually farther from the centre than those of the mounting side, and yet equal in number and heft of the one side as the other. A most incredible thing, if not seen, but tried before the late king of happy and glorious memory, in the Tower, by my directions; two extraordinary ambassadors accompanying his Majesty, and the Duke of Richmond, and Duke Hamilton, with most of the court attending him. The wheel was fourteen feet over, and forty weights of fifty pounds a-piece. Sir William Belford, then Lieutenant of the Tower, can testify it, with several others. They all saw, that no sooner these great weights passed the diameter line of the upper side, but they hung a foot farther from the centre; nor no sooner passed the diameter line of the lower side, but they hung a foot nearer. Be pleased to judge the consequence. NOTE.