Theatrum naturae et artis

(a) Which arise from the threefold application of points: A. the motive power, B. the hypomochlion original: "hypomochlii" or fulcrum, and C. the weight to be moved: A B C A C B : B A C. The proportion of the weight to be moved to the motive force is such, as that of the longer arm to the shorter. The lever is illustrated by various examples, namely: two glasses upon which a rod is placed, though the rod must be broken by a strike while the glasses remain safe; two people bearing some weight either equally or unequally; an oar in a boat and the mast in the same; forceps; a claw hammer; molar teeth, etc.

(b) Regarding the various structure and position to be considered, it is still always nothing other than a continuous lever, or as many levers as there are radii in the circumference of a wheel; hence the same rule holds here as previously regarding the power of the lever.

(c) Namely, a monospastos single-pulley system where there is one pulley; and if another is added, it is merely for convenience. Just as a rope is urged into equal parts, so also the gravity of the weight is divided into two equal parts: then a dispastos two-pulley system, where there are two pulleys in the lower part and as many in the upper, though not by necessity: hence the weight is distributed into four equal parts: furthermore, a trispastos three-pulley system, where three pulleys are held in the upper part and three in the lower, and thus the weight is divided into six equal parts. The common rule for all of these is: The motive virtue is multiplied according to the number of ropes sustaining the weight.

(d) The power of which is estimated, in the traction of a weight, by the proportion of the hypotenuse to the perpendicular.