Questions.

Why does the flame, in running to its place, make itself pyramidal, while the water rounds itself in its descent — that is, at the extremity of the drop?

m

n, a b

m, n, S

Consider the position of these two handles, and observe the motion that the lower handle wishes to make, going toward the left hand. See that it goes declining, and the upper handle would wish to rise, and the length of the connecting-bar does not allow it, whence it turns back. If, by cause of turning one of these handles, you should wish the other together with it to give a full turn, you will deceive yourself. For when the handle S were itself the prime mover, and were found in the position you see, the other one above will not give a full turn like the first, because it does not pass the perpendicular line of the centres of their poles. Whence it has more ease in turning back than in following the full turn. But if by chance it did go forward, it will often stop most firmly, when the line that goes from the centre of the pole to the centre of the ring becomes all one thing with the central line that passes through the connecting-bar going from the one handle to the other.

If you turn the handle here in the middle in a round turn, all the handles that could be attached to the iron, called the connecting-bar, would turn a full turn together with the prime-mover handle. But if you wished to do the like by turning the lower or the upper handle, this that has been said would not succeed for you except most rarely. For when the lower handle turns to the left, the one above desires to turn in the contrary direction, as if wishing to make itself the pole of the middle handle — as the other figure placed in the middle does — whence it would succeed for you most rarely. But if there were more than three, it would do better, because the connecting-bar would then have no pole in the middle.

It is impossible, with the handle m, to turn the upper handle n without the help of a b. And the circles that you see at head and at foot show the path of the motion that the handle makes as it turns about its fixing. The 6 lines show 6 positions of the iron that goes from the one handle to the other.

a n, m, S

In this one none of the defects said above occurs, because the handle a n is not subject to giving a full turn, as m S is.