Page:Popular Science Monthly Volume 11.djvu/182

170. The principle that the state of "expectant attention" is capable of giving rise either to sensations or to involuntary movements, according to the nature of the expectancy, had been previously recognized in physiological science, and was not invented for the occasion; but the phenomena I have been describing to you are among its most "pregnant instances."

The same principle furnishes what I believe to be the true scientific explanation of the supposed mystery of the divining-rod, often used where water is scarce for the discovery of springs, and in mining-disstrictsdistricts [sic] for the detection of metallic veins. This rod is a forked twig shaped like the letter Y, hazel being usually preferred; and the diviner walks over the ground to be explored, firmly grasping its two prongs with his hands, in such a position that its stem points forward. After a time the end of the stem points downward, often, it is said, with a sort of writhing or struggling motion, especially when the fork is tightly grasped; and sometimes it even turns backward, so as to point toward instead of away from the body of the diviner. Now, there is a very large body of apparently reliable testimony, that when the ground has been opened in situations thus indicated, either water-springs or metallic veins have been found beneath; and it is quite certain that the existence of such a power is a matter of unquestioning faith on the part of large numbers of intelligent persons who have witnessed what they believe to be its genuine manifestations. This subject, however, was carefully inquired into more than forty years ago by MM. Chevreul and Biot; and their experimental conclusions anticipated those to which I was myself led in ignorance of them by physiological reasoning. They found that the forked twig cannot be firmly grasped for a quarter of an hour or more in the regulation position, without the induction of a state of muscular tension, which at last discharges itself in movement; and this acts on the prongs of the fork in such a manner as to cause its stem to point, either upward, downward, or to one side. The occasion of this discharge and the direction of the movement are greatly influenced, like the oscillations of bodies suspended from the finger, by expectancy on the part of the operator; so that if he has any suspicion or surmise as to the "whereabouts" of the object of his search, an involuntary and unconscious action of his muscles causes the point of the rod to dip over it.

Again, since not one individual in forty, in the localities in which the virtues of the divining-rod are still held as an article of faith, is found to obtain any results from its use, it becomes obvious that its movements must be due, not to any physical agency directly affecting the rod, but to some influence exerted through its holder. And that this influence is his expectation of the result may, I think, be pretty confidently affirmed. For it has been clearly shown, by careful and