Note 11 — APPENDIX.

In recent works the word energy is used to designate active or working force as distinguished from passive or non-working force. It is in this working condition only that force is conserved, and therefore conservation of energy is the proper expression. Nevertheless, since the distinction between force and energy is imperfectly or not at all defined in the higher forms of force, and especially in the domain of life, I have preferred in this article to use the word force in the general sense usual until recently.