HYDRODYNAMICS AND ELECTRICITY. 255 



pole. If, now, having one of the drums mounted in the water, and 

 the other held in the hand, we bring them near each other while both 

 are dilating or both are contracting that is, while both are in the 

 same phase of pulsation attraction will take place between them. 

 The mounted drum will assume the direction of approach toward the 

 one held in the hand, and of following it when it is removed ; but if 

 they are in opposite phases if one is swelling while the other is con- 

 tracting they will be repelled. Like poles attract, unlike ones repel. 

 The phenomena are the inverse of what are observed in ordinary elec- 

 tricity and magnetism, where unlike poles attract and like ones repel. 

 The pulsating drum in these experiments represents an isolated pole, a 

 conception which physicists have not hitherto regarded as possible. 



Spheres of invariable volume, but adjusted so as to oscillate in either 

 an horizontal or vertical direction, maybe used instead of the pulsating 

 drums, when the phenomena assume a modified shape. The oscillators 

 used by Professor Bjerknes are mounted as in the figure (Fig. 1, 3), 

 where the sphere on the left is arranged so as to oscillate horizontally, 

 and the one on the right to oscillate vertically, the alternate move- 

 ments of oscillation being produced, like the pulsations of the drums, 

 by alternately forcing in and withdrawing the air. The opposite sides 

 of the sphere assume opposite phases, and the sphere acts like a mag- 

 net. If a sphere is brought near a pulsator, so that its oscillating 

 movement shall be toward the drum while that is dilating, attraction 

 takes place ; but, if it be turned in the opposite direction, so as to be 

 moving away from the drum while the same is swelling, repulsion will 

 be manifested. 



If two oscillating spheres be brought near each other, attraction 

 takes place in case they are both moving to or from each other; repul- 

 sion, in case they are both moving in the same direction : and the 

 change can be effected at once, as before, by turning one of the spheres 

 around. 



Professor Bjerknes has a considerable variety of apparatus for 

 modifying the aspects of the phenomena by changing the relative 

 situations of the bodies to each other, in all of which manifestations 

 of an inverse character to those of ordinary magnetism are developed. 

 If one of the spheres be mounted so as to be free to move about a 

 vertical axis, it is found that, when a second oscillating sphere is 

 brought near to it, the one that is free turns round its axis, and sets 

 itself so that both spheres shall be simultaneously approaching or re- 

 ceding^ from each other. Two oscillating spheres mounted at the ex- 

 tremities of an arm, with freedom to move, behave with respect to 

 another oscillating sphere exactly like a magnet; in the neighborhood 

 of another magnetic pole. These directive effects are believed by 

 Professor George Forbes to be perfectly new, both theoretically and 

 experimentally. 



The phenomena* of attraction and repulsion, described above, are 



