for sparrows. But there is nothing irrational in believing that a power which is seen to be intelligent where we can comprehend its action, is also intelligent in realms where we cannot detect any purpose. Nevertheless, it must be allowed that the final purpose for which all lower ends exist, that "far-off divine event to which the whole creation moves," is not revealed to our knowledge, but to our faith. We would use great reticence, therefore, in speaking of the divine purposes, for a sufficient insight is lacking. Least of all, would we have physical science diverted from its study of phenomenal laws in order to search for final causes. Such a course could result only in religious and scientific scandal. There are two ideals toward which the mind strives: first, to know how every thing is done; and, second, to know what it is done for. Both ideals are unattainable at present; but the study of the methods of nature is practically of vastly more importance in physical science than a study of the purpose of things. It is with our belief in purpose, as with our faith in a divine providence. If this faith be attacked, we are ready to show that there is no reason for being ashamed of it. And yet from no feeling of shame, but from reverence rather, we prefer not to have that great name too often upon our lips, but content ourselves with believing that our times are in God's hand without specifying too curiously how he is working out his will concerning us.

CHAPTER V.

THE CONSERVATION OF ENERGY.

THE HE man who journeyed from Jerusalem to Jericho fell among thieves. The doctrine of the conservation of energy has been still more unfortunate; it has fallen a prey to the magazine scientists and rhetoricians. These have stripped it of its true meaning, and saddled false ones upon it, until scarcely any likeness to its scientific self remains. "We read constantly," says Professor Tait, "of the so-called 'physical forces'-heat, light, electricity, etc.; of the 'correlation of the physical forces,' the 'persistence or conservation of force.' To an accurate man of science, all this is simply error and confusion." ""* These misunderstandings of the doctrine have given great support to materialism and atheism. Hence the need of examining the subject.

The doctrine in question was first known as the correlation and conservation of the forces. The forces were said to correlate, and hence force is one. Force was also said to be conserved, and hence was presumably eternal. But this terminology was treacherous; for force is defined in text-books on physics and mechanics as any thing which tends to change the condition of a body whether in motion or at rest. Hence, gravity, cohesion, affinity, repulsion, pressure, impact, etc., were all

*"Recent Advances in Physical Science," p. 389.

arranged under the head of force. Now, as the forces. were said to correlate, it was easy to blunder into the notion that all the attractive and repulsive forces of matter can pass into one another. It was not uncom

All

mon to hear it asserted that chemical affinity, and even repulsion, were but transformed gravity. Even the space-filling quality of matter depends upon force; and since all the forces correlate, it occurred to some speculators that solidity and inertia also must, in some way, correlate with the other forces. Other speculators, whose ignorance was equally dense and exhaustive, urged that this would never do; as in such case matter might go off in a puff, and thus nothing would be left. This necessity of limiting the correlation, was felt as a great hardship by the more radical speculators; and was regarded as a victory by the conservatives. The discussion was mainly a logomachy without a ray of insight into the scientific meaning of the doctrine. things are phenomena of force; and are not gravity and repulsion, and life and mind and matter and every thing, forces? How, then, can we deny their correlation? With this understanding of the doctrine, Mr. Herbert Spencer proceeded to prove a rich variety of propositions, such as the indestructibility of matter, the continuity of motion, the correlation and equivalence of physical and mental force, the impossibility of freedom, and divers sociological laws. Mr. Bain found in it the reason why one cannot attend to many things at once, or become great in many directions. So terrible are the ravages in physics of arguing from words without attending to their scientific content.

The doctrine of the constancy of force suffered no less from this verbal exegesis. Inasmuch as force is constant, what shall we make of the fact that all the attractive and repulsive forces vary with the distance across which they act, so that while their law is constant, they themselves are incessantly varying? In the case of gravity, a body at half the distance acts with four times the energy; at double the distance, it acts with only one fourth of the energy. Whence the gain and loss of power? Since force is constant, the idea of creation or destruction is inadmissible; whence, then, the increment, and whither the decrement? No less a man than Faraday was sent off on a wild-goose chase by reasoning of this sort; and he concluded that it must come from, and return to, the ether-that limbo of scientific difficulties. He argues at length that without some such assumption we come in hopeless conflict with the doctrine of conservation.* Strangely enough, it never seems to have occurred to him that this result bordered on a reductio ad absurdum of the conservation

doctrine.

Inasmuch as

In like manner the doctrine that work involves the expenditure of force was misunderstood. an attracting body is forever pulling at all the rest of the universe, it occurred to many speculators that the

.attracting

forces of the elements must be wearing out.

They have already pulled the matter of our solar system through vast spaces, and condensed it into comparative

ly very

small

spaces.

Now as a vast amount of work

*See his paper in "The Correlation and Conservation of Forces."

D. Appleton & Co.

has been done; and as work involves the expenditure of force, of course the attractions are growing less and less. Opposed to this conclusion, however, was the awkward fact, that, in truth, the attractions are now stronger than ever before; and thus the doctrine of conservation was again endangered. To escape this difficulty, some speculators imagined that motions may become attractions or repulsions, and conversely. That motion implies something which moves, and attraction something which attracts, and that a moving thing, as such, is not an attracting thing, was a fact of which they had not the slightest suspicion. This impossible identification of motion and attractive or repulsive force seems to underlie the following extraordinary statement by Mr. Grove, whose treatise upon the correlation of the physical forces is popularly supposed to be classical:

"Of absolute rest nature gives us no evidence. All matter, as far as we can ascertain, is ever in movement, not merely in masses, as with the planetary spheres, but also molecularly or throughout its most intimate structure, so that, as a fact, we cannot predicate of any portion of matter that it is absolutely at rest. Supposing, however, that motion is not an indispensable function of matter, but that matter can be at rest, matter at rest would never of itself cease to be at rest; it would not move, unless impelled to such motion by some other moving body or body which has moved. This proposition applies not merely to impulsive motion, as when a ball at rest is struck by a moving body, or pressed by a spring which has previously been moved,