A way to remove to and fro huge weights, with a most inconsiderable strength, from place to place. For example: ten ton with ten pounds, and less; the said ten pounds not to fall lower than it makes the ten ton to advance or retreat upon a level. NOTE. A weight attached to an ordinary crane may be moved with the utmost facility; and it is well known that the employment of friction wheels furnishes a ready medium of conveyance for masses of iron and stone of the greatest magnitude. No. XXVIII. A bridge, portable upon a cart, with six horses, which, in a few hours' time, may be placed over a river half a mile broad, whereon, with much expedition, may be transported, horse, foot, and cannon. NOTE. A portable bridge, or rather ferry boat, calculated for crossing wide and deep rivers, was frequently employed in ancient warfare, and is still used for the conveyance of horses and passengers in many parts of Europe. The apparatus for this purpose may readily be attached to the banks of the most rapid river, as it merely consists in the employment of two ropes or wires, tightened by means of a winch, on which slide pullies connected with a large floating tank or waggon, that is afterwards intended to be employed as a medium of conveyance. The apparatus being thus prepared, a communication may readily be opened by means of two cords between the opposite banks of the river. No. XXIX. A portable fortification, able to contain five hundred fighting men, and yet, in six hours' time, may be set up and made cannon proof, upon the side of a river or pass, with cannon mounted upon it, and as complete as a regular fortification, with half-moons and counterscarps. NOTE. It is difficult to attempt an elucidation of this or the following articles; but the annexed extract from the _General Evening Post_ for 1747 appears to throw some light on No. XXX. "On the 11th instant, Mr. James Allis was presented to the Royal Society, with a new invented cannon, which charges and discharges both at one time, and twenty times in a minute: he had their thanks, and a handsome present." No. XXX. A way, in one night's time, to raise a bulwark, twenty or thirty foot high, cannon proof, and cannon mounted upon it; with men to overlook, command and batter a town; for, though it contain but four pieces, they shall be able to discharge two hundred bullets each hour. NOTE. Vide the preceding Article. Since writing the above, the Editor has been called to witness the effects of highly elastic vapour applied to the propelling of leaden bullets, in an apparatus contrived by Mr. Perkins; and these destructive missile engines are capable of discharging nearly two hundred bullets, in one sixtieth part of the time described by our author in the present Article. No. XXXI.