# Popular Science Monthly/Volume 6/February 1875/Correspondence

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ALLEGED FALLACIES OF SCIENCE—CAUSE AND EFFECT—MODES OF FORCE.
To the Editor of the Popular Science Monthly:
DR. JOHN W. DRAPER'S "History of the Conflict between Science and Religion" should be read by every searcher after truth. But Dr. Martineau's address in London, last fall, on "Religion as affected by Modern Materialism," considered in connection with Dr. Draper's book, portends danger to the dogmatic assertion of mere hypotheses, or guesses, as scientific facts. Enlightened people are fond of sensation as a pastime, but, in the serious and desperate conflict which is surely approaching, they will accept neither superstition nor sophistry, but only mathematical truth or pure logic. Scientific imagination, useful in research, should not be allowed to culminate in illogical speculation. Phenomena are effects: and not their causes, but only their correlates or conditions under which they occur, lie in the field of physical science.
Physical force is not the cause of physical action. Specific modes of force have no physical existence, but are only in thought correlatives to phenomena. Gravity is not the cause of the persistent movement of cosmical bodies, nor of their relative positions to each other, nor is it a physical "thing;" it is only one of the many correlates in thought, of the ever-changing relative positions of these bodies.
Physical force or pressure has no generalized mechanical equivalent. Like quantities of mechanical effect, due to like quantities of any mode of force, are limited to exact conditions.
The fact that mere physical force or pressure is not the cause of motion, and has no quantitative equivalent in mechanical effect, is mathematically demonstrated thus:
Under the gravity or pressure of the atmosphere—fifteen pounds to the inch—water has a velocity of forty feet per second, and steam, or other gas of like density, a velocity of 1,600 feet. Hence, considering the relative velocities and masses, the mechanical effect observed with reference to the gas is forty times that with reference to the water, both substances acting under the same pressure during the same time. (Space, never having been alleged to be a cause, is purposely neglected in this calculation. As a correlate of phenomena, it will form the subject of a future communication.) These varying effects obtain whenever unlike masses move under like qualities of constant force. Therefore, as cause equals effect, the mechanical effects, proportional to mass, being quantitatively different under the same force, they cannot be caused by the pressure or force under which they act.
Hence, that scientific imagination which treats modes of force as causes, and from this hypothesis, and exactly conditioned experiments, generalizes the quantitative equivalent effect of any one mode—as the "mechanical equivalent of heat"—and from similar hypotheses calculates the densities, temperatures, etc., of other worlds than ours, is not in accordance with mathematical demonstration, and is, therefore a delusion. "Promise and potency" are causes, and, as Prof. Tyndall very properly says, are discerned in matter; and, being absolutely known, they are not susceptible of proof. But their effects, being only observed, and therefore conditioned, are susceptible of both proof and prediction from knowledge of the several conditions under which they arise. Pure science adduces not the causes, but only these conditions of phenomena.
The times portend a crisis in one of Mr. Herbert Spencer's rhythms which has long been setting in, laden with sophistry, miscalled expediency, and general demoralization. Let pure science, resolutely, but carefully, take advantage of its ebb.
* A. Arnold
* Tenafly, N. J., December 28, 1874.