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THE POPULAR SCIENCE MONTHLY. 



supposed by Professor Bjerknes and Professor Forbes to be due, not 

 to the action of one body on the other, but to the mutual action of one 

 body and the water in contact with it, the water being regarded as 

 the analogue of Faraday's medium. "Viewed in this light," says 

 Professor Forbes, " his first experiment is equivalent to saying that, if 

 a vibrating or oscillating body have its motions in the same direction 

 as the water, the body moves away from the center of disturbance ; 

 but, if in the opposite direction, toward it. This idea gives us the 

 analogy of dia- and para-magnetism. If, in the neighborhood of the 

 vibrating drum, we have a cork ball, retained under the water by a 

 thread, the oscillations of the cork are greater than those of the water 

 in contact with it, owing to its small mass, and are, consequently, rela- 

 tively in the same direction. Accordingly, we have repulsion, corre- 

 sponding to diamagnetism. If, on the other hand, we hang in the 

 water a ball which is heavier than water, its oscillations are not so 

 great as those of the water in its vicinity, owing to its mass, and con- 

 sequently the oscillations of the ball relatively to the water are in the 

 opposite direction to those of the water itself, and there is attraction 

 corresponding to para-magnetism. A rod of cork and another of 

 metal are suspended horizontally by threads in the trough, and a vi- 

 brating drum is brought near them : the cork rod sets itself equatori- 

 ally, and the metal rod axially." 



Fig. 2. 



From these and other experiments Professor Bjerknes has con- 

 cluded that the motion of a vibrating agent in the water produces a 

 real magnetic field, with its lines of forces presenting, but always 

 in an inverse sense, identical phenomena of diamagnetism and para- 



