Correspondence — Professor M. E. Wadsworth. 239 



paracme of SonninincB ; during the second, the predominance of 

 Fai-hinnonicB. 



The paper contains a hemeral timetable of the Eojurassic Period 

 and part of the Neojurassio, a genealogical table of Ammonite 

 development daring the same and a previous portion of time, notes 

 on certain generic names, and a list of the Ammonite genera 

 referred to. 



OOS/IRESI^OiTZDSilNrOIE. 



A MECHANICAL THEORY OF THE DIVINING -ROD. 



The review in Nature (1897, pp. 668, 569) of a publica- 

 tion relating to the " divining-rod," recalls to my mind a purely 

 mechanical theory of that rod, which was given me years ago by 

 a friend. 



This theory has been repeatedly tested by me and shown to bo 

 correct in the presence of my classes. The process is exceedingly 

 simple. Take any forked twig of a reasonably tough fibre in tlie 

 clenched hands with the palms upward. The ends of the limbs 

 forming the twig fork should enter the closed fists on the exterior 

 side of each fist, i.e. on the two sides of the clenched hands furthest 

 from each other. 



When a twig is grasped in this position it will remain stationary 

 if held loosely, or with only a moderately firm grasp : but the 

 moment the grasp is tightened, the pressure on the branches will 

 force the end of the twig to bend downwards. The harder the grip 

 the more it must curve. 



The curvature of the twig is mechanically caused by the pressure 

 of the hands forcing the limbs to assume a bent and twisted position ; 

 or the force that causes the forked limb to turn downwards is 

 furnished by muscles of the hands, and not from any other cause. 



The whole secret of the " divining-rod " seems to reside in its 

 position in the hands of the operator, and in his voluntarily or 

 involuntarily increasing the closeness of his grasp on the two ends 

 of the branches forming the fork. 



If the above conditions are fulfilled the twig will always bend 

 downwards — water or no water, mineral or no mineral ; anyone 

 can be an operator, and any material can be used for the instrument, 

 provided the limbs forming the fork are sufficiently tough and 

 flexible. 



It can be easily understood how an ignorant operator may deceive 

 himself, and be perfectly honest in supposing that some occult force, 

 and not his hands, causes the fork to curve downwards. 



M. E. Wadsworth. 



Michigan College of Mines, Houghton, Michigan. 



