Page:The Mathematical Principles of Natural Philosophy - 1729 - Volume 1.djvu/109



In non-reiting paces or mediums, if the areas are not proportional to the times, the forces are not directed to the point in which the radii meet; but deviate therefrom in conequantia, or towards the parts to which the motion is directed. if the decription of the areas is accelerated; but in antecedentia, if retarded.

And even in reiting mediums, if the decription of the areas is accelerated, the directions of the forces deviate from the point in which the radii meet, towards the parts to which the motion tends.

A body may be urged by a centripetal force compounded or everal forces. In which cae the meaning of the propoition is, that the force which reults out of all, tends to the point S. But if any force, acts perpetually in the direction of lines perpendicular to the decrib'd urface; this force will make the body to deviate from the plane of its motion: but will neither augment nor diminih the quantity of the decribed urface, and is therefore to be neglected in the compoition of forces.