344 Dynamic Theory. 



Mr. Stroh, following the hint given by these experiments in water, 

 performed a series of similar ones, using air as the fluid to be thrown 

 into motion, and musical reeds in tubes as instruments for communi- 

 cating regular vibrations to small drum-heads. He got practically the 

 same results as those of Prof. Bjerkness. His vibrating drums attracted 

 each other when vibrating in the same phase, and repelled when vibrat- 

 ing in opposite phases. He found the lines of force by using a small 

 gas jet, which could be moved about the field. When two drums were 

 vibrated in like phase, and this flame held between them, it was repelled 

 at right angles from their axis. If such flame be held between the dis- 

 similar poles of a powerful electro-magnet, it will be repelled in the 

 same way. Mr. Stroh says that if magnetism is due to the vibration of 

 a medium his experiments lead to the conclusion that the rate of such 

 vibration must be identical in all magnets, and that this rate, in fact, 

 constitutes magnetism as distinguished from other electrical phenomena. 

 That magnetism is a vibration of a medium like ether, he says, is strongly 

 favored by its analogy with vibrating bodies, although the effects ap- 

 pear to be inverse throughout. It is quite obvious that if the magnetic 

 action is due to a motion of a medium, the experiments did not pre- 

 cisely imitate it. 1 



Where a current passes from one pole to another it possesses carrying 

 powers. This is well shown in electrotyping, in which currents passed 

 through a solution of sulphate of copper, for example, will pull the cop- 

 per away from the sulphur and carry it to the negative pole, while the 

 rest of the compound will be carried to the positive pole. A remark- 

 able story was told by the papers not long ago, of a thunderbolt which 

 electro-plated a cat with silver. The cat was sleeping on a sofa, so the 

 story goes, above which hung an old fashioned, silver hilted sword. 

 The lightning traversed the partition on which the sword hung, dis- 

 solved the silver which it carried through the air and left neatly coat- 

 ing every hair of the cat, while it continued on its way to the ground. 

 If this be fiction, it is not more remarkable than the truth. The pro- 

 jection of currents must mean the bodily movement of a physical body 

 throwing itself into another body of the same substance at rest. The 

 experiments mentioned above, produced motion in this latter body with- 

 out taking account of the currents by which the motion is produced, in 

 the case of magnetism and electricity. It was mentioned above that 

 heat may produce or become an electrical current. In like manner an 

 electrical current is, in part, converted into heat, whenever it passes 

 through a metal, but not to the same extent in any two. The follow- 

 ing table shows the conducting power of various metals, calling 



1 An account of these instructive researches may be found in Gordon's Electricity and 

 Magnetism, 



