170 THE POPULAR SCIENCE MONTHLY. 



fested. The principle that the state of " expectant attention " is 

 capable of giving rise either to sensations or to involuntary move- 

 ments, 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-dis- 

 stricts 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 unques- 

 tioning 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 conclu- 

 sions 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 liour 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 " where- 

 abouts " 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 tliink, be pretty 

 confidently aftirmed. For it has been clearly show'n, by careful and 



' I have lately received a pamphlet from an engineer in the United States, giving 

 most circumstantial details of success thus obtained within his own experience. 



