Comment by Pigafetta
Here one may note that the author has not gone into these last instrumentsÑthat is, the wedge and the screwÑas he did the lever, the pulley, and the wheel and axle, for which he has very exactly shown the ratio of the force and weight.This is because these two instruments in themselves are not suitable to be considered as sustaining a weight, but rather as moving it.Now, since the powers that move may be infinite, one cannot give a firm rule for them as may be done for the power that sustains, which is unique and determined.That the wedge- is not suitably considered as sustaining is clear in itself, and that the same is true of the screw is evident in the ordinary uses of the screw to move weights--- Thus the author has dealt with the two last instruments as suits their nature, as he says in comparing together all five of the instruments for moving weights as a conclusion to his work.
The End