What force is. Force, I say, is a spiritual power, incorporeal and invisible, which with brief life is caused in those bodies that, through accidental violence, stand outside their natural being and rest. Spiritual I called it, because in this force there is active life; incorporeal and invisible I say, because the body in which it is born grows neither in weight nor in form; of little life, because it always desires to overcome its cause, and that once overcome, it kills itself.

a g - b - f c d e

If you wish to know how much weight the stick of eight pounds and four braccia gives to the wall a c and how much to the point e, do thus. Divide in half the base of the triangle a c e, which will be d e, and as much as that part occupies of the upper part of the stick, so much weight remains on the wall a c, and the rest goes to e. The body whose length exceeds and surpasses its breadth and depth must distribute a greater sum of its heaviness to the lower part that descends from its horizon than to the upper. But if that body lies with its two extremities on the horizon, its two ends must be of equal heaviness at their contacts, when the body is of equal thickness and weight throughout its length.

n. That body whose continuous breadth is surpassed by its length must give equal load to its two extreme contacts when they are equidistant from the centre, as f e. But when the body stands on a perpendicular line, I say the contact of the lower extremity receives upon itself all the load set above, and the upper weighs nothing on its opposite contact, as appears in g e. But if that body has its two ends at unequal distance from the said centre, it will be of unequal weight, because the part that draws nearer loads more, and the more distant becomes lighter, as appears in a e. Therefore, if in the first proposition the weight is shown to divide itself at its two extreme contacts f e, and in the second the lower e receives all and the upper g nothing, then one must confess, by geometric and arithmetic reasoning, that the weight found between the one and the other mode shares between the two extremes, as a e. If the weight a e be 4 braccia and 8 pounds, and you hang it so that it is not all at the point e, nor divided in half at f e, but is found at the middle of the line f e, that is above the point c, I say by arithmetic reasoning that if the weight, standing upright, gives 8 pounds of load to the point e, and lying wholly flat gives it 4, now take the mean between 4 and 8, which is 6; therefore the point e is 6, and c a is 2, between force and weight. And by geometric reasoning it is found that, taking the base of the triangle a c e and dividing it in half at the point d, I say d e is always given to a c, and d f is given to e; d e is like a b, and d f is like b e.