152 Contributions to Electricity and Magnetism. 



the shock increased by spreading a stratum of oil over the sur- 

 face of the mercury ; in this case it is probable that the termina- 

 tion of the current is more sudden, on account of the preven- 

 tion of the combustion of the metal by means of the oil, and the 

 fact that the end of the conductor is drawn up into a non-con- 

 ducting medium. 



91. The time of the subsidence of the current, when the cir- 

 cuit is broken by means of a surface of mercury, is very small, 

 and probably does not exceed the ten thousandth part of a sec- 

 ond, but even this is an appreciable duration, since I find that the 

 spark at the ending presents the appearance of a band of light of 

 considerable length, when viewed in a mirror revolving at the 

 rate of six hundred times in a second ; and I think the variations 

 in the time of ending of the current under different conditions 

 may be detected by means of this instrument. 



92. Before concluding this communication, I should state that 

 I have made a number of attempts to verify the suggestion given 

 in my last paper, (III, 127,) that an inverse induction is produced 

 by a galvanic current by a change in the distance of the conduc- 

 tors, but without success. These attempts were made before I 

 had adopted the views given in this section, and since then I 

 have found (80) a more simple explanation of the alternation of 

 the currents. 



93. In this number of my contributions, the phenomena ex- 

 hibited by the galvanic apparatus have alone been discussed. I 

 have, however, made a series of experiments on the induction 

 from ordinary electricity, and the reaction of soft iron on currents, 

 and I think that the results of these can also be referred to the 

 simple principles adopted in this paper; but they require further 

 examination before being submitted to the public. 



