Let no one from the above views, or from similar views expressed by others, draw hasty conclusions in favor of a pure materialism. Force and matter, or spirit and matter, or God and Nature, these are the opposite poles of philosophy--they are the opposite poles of thought. There is no clear thinking without them. Not only religion and virtue, but science and philosophy, cannot even exist without them. The belief in spirit, like the belief in matter, rests on its own basis of phenomena. The true domain of philosophy is to reconcile these with each other. FOOTNOTES: [11] 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. [12] _American Journal of Science_, November, 1859. _Philadelphia Magazine_, vol. xix., p. 133. [13] In 1845 Dr. J. R. Mayer published a paper on “Organic Motion and Nutrition.” I have not seen it. [14] For more full account, see my paper, _American Journal of Science_, November, 1859, sixth and seventh heads. [15] _American Journal of Science_, November, 1872. The experiments of Dr. Draper are inconclusive, because they are made on _seedlings_, which, until their supply of organic food is exhausted, are independent of sunlight. [16] I might add still another plane and another force, viz., the human plane, on which operate, in addition to all the lower forces, also free-will and reason. I do not speak of these, only because they lie beyond the present ken of inductive science. [17] _Archives des Sciences_, vol. xlv., p. 345, December, 1872. CORRELATION OF NERVOUS AND MENTAL FORCES. BY ALEXANDER BAIN, LL. D., PROFESSOR OF LOGIC AND MENTAL PHILOSOPHY IN THE UNIVERSITY OF ABERDEEN. THE CORRELATION OF NERVOUS AND MENTAL FORCES.