18. In hard bodies, therefore, which are compressed or extended, if, that which compresseth or extendeth them being taken away, they restore themselves to their former place or situation, it must needs be that that endeavour or motion of their internal parts, by which they were able to recover their former places or situations, was not extinguished when the force by which they were compressed or extended was taken away. Therefore, when the lath of a cross-bow bent doth, as soon as it is at liberty, restore itself, though to him, that judges by sense, both it and all its parts seem to be at rest; yet he, that judging by reason doth not account the taking away of impediment for an efficient cause, nor conceives that without an efficient cause any thing can pass from rest to motion, will conclude that the parts were already in motion before they began to restore themselves. [Sidenote: Action and reaction proceed in the same line.] 19. _Action_ and _reaction_ proceed in the same line, but from opposite terms. For seeing reaction is nothing but endeavour in the patient to restore itself to that situation from which it was forced by the agent; the endeavour or motion both of the agent and patient or reagent will be propagated between the same terms; yet so, as that in action the term, _from which_, is in reaction the term _to which_. And seeing all action proceeds in this manner, not only between the opposite terms of the whole line in which it is propagated, but also in all the parts of that line, the terms _from which_ and _to which_, both of the action and reaction, will be in the same line. Wherefore action and reaction proceed in the same line, &c. [Sidenote: Habit, what it is.]