Of most things that exist, if not of all, let us say that they are capable of existing in either of two states--the dynamical or the statical--and that, when viewed as dynamical, they are forces or powers; when viewed as statical, they are substances. When we exhaust or think away the properties of existence, the last which vanishes is self-manifesting power in the object which exists, this property being such that when it vanishes so does the object to which existence was awarded. In the science of the day it is maintained by our most popular authors and lecturers that the "physical forces"--taken in the singular number, physical force--is the last word, the ultimate principle. The physical forces are represented as all that there is for God, whereas they are but as the fingers of God. The idea of antecedent design, either in reference to nature as a whole, or in reference to any object in particular, is dropped as unscientific, or repudiated as unsound; in short, a reference to the physical forces, is the last word permitted in any treatise, if that treatise is to be admitted as possessing a scientific character. Or, if there be one word more, it is only the "correlation" of those same physical forces, and their "conservation," or persistence eternally in the same amount of energy in the universe. In their own place and within their own sphere, these are physical truths, which are of the greatest value. The former is a wholesome relapse into the old philosophy of nature. The latter is also a return to a view which is more sound than that which was popular before the doctrine of conservation was resuscitated. Descartes' opinion, that there was a conservation of motion in the universe, was demonstrated by Newton to be a mistake. Leibnitz adjusted the truth between these great men, showing that it was not motion, but the possibility or means of motion--in one word, energy--that was conserved in the universe. The doctrine of the conservation of energy amounts to nothing more than this, that inasmuch as every ultimate atom of matter is perfectly elastic, so is the whole universe of atoms perfectly elastic. Hence it is a doctrine which cannot be legitimately extended beyond the merely material sphere; except on the assumption that matter is the only reality, and that there is no such thing as a spiritual world at all--an assumption which, however often it has been made, serves only to awaken a prevailing voice to the contrary, and the firm vote of a large majority to the effect that mind exists as well as matter.