On Natural Motions Depending on Gravity

ON NATURAL MOTIONS Made by Gravity

SUPPOSITION I.

I suppose first that any body, whether dense or fluid, among those that compose the terraqueous globe A term used by early modern scientists to describe the Earth as a single sphere made of both land and water., is heavy. It exerts the force or effort original: "conatum." In 17th-century physics, this refers to a body's internal tendency or "striving" to move in a certain direction. of its gravity even if it is placed in a fluid that is either of the same nature as itself or different. This will be confirmed in its proper place with very evident reasons and experiments.

SUPPOSITION II.

In the second place, I suppose that the force, or effort, by which fluids strive to join themselves to the terraqueous sphere, acts along lines perpendicular to the surface of the horizon. This is evident because any heavy body, by natural instinct, strives to reach the center of the earth by the shortest path. Therefore, the direction of this motion, or the compressive effort, occurs along the radii original: "semidiametros." Borelli refers to lines drawn from the center of the Earth to its surface. of the earth. These lines are perpendicular to the horizontal surface that surrounds the earth like a sphere. Thus, it is clear that the motion or compressive effort of all parts of a fluid acts along lines perpendicular to the horizon.

SUPPOSITION III.

Thirdly, it is impossible for any heavy body to move with a spontaneous and natural motion when it cannot get any closer to the center of the earth. This is clear because all earthly parts, being heavy, strive by natural instinct to reach the center of the earth