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PREFACE.

For a long time now, the word "Mechanics" has held a double meaning, and indeed at this time two sciences are called by that name which are entirely different from each other, both in their principles and in their subject matter. For the name "Mechanics" is usually assigned to that science which deals with the equilibrium of forces potentiae: literally "powers," here referring to the forces or pressures that act upon bodies and their comparison with one another; but it is also given to that science in which the very nature, generation, and alteration of motion is explained. For although forces are also primarily considered in this latter discipline—since motion is both generated and changed by them—the method of treatment differs greatly from the former science. Therefore, to avoid all ambiguity, it will be helpful to call that science which deals with the equilibrium and comparison of forces "Statics," while reserving the name "Mechanics" solely for the other, the science of motion—