256 Dr. A. Schuster on Unilateral Conductivity. 



circuit, the wire showed a very strong unilateral conductivity. 

 Cleaning and scraping the wire had at first apparently no effect; 

 screwing the wire, however, to another binding-screw attached 

 to the induction-coil destroyed the effect entirely, so that the 

 wire, even when screwed to the original binding-screw, showed 

 no unilateral conductivity. The same experiment was repeated 

 a second time, and with the same result. Five minutes'' lying 

 in powdered charcoal was sufficient to reproduce a strong 

 unilateral conductivity; and the same operation as before 

 destroyed it. 



VI. Failure of the Theory, 



A third trial to obtain unilateral conductivity by the same 

 means failed. The wire was put into the charcoal for several 

 hours instead of several minutes ; but even then it remained in 

 its neutral state. All the various circumstances which generally 

 had produced unilateral conductivity were now tried ; but none 

 succeeded. New wires were tried; the whole apparatus was 

 left untouched and disconnected for several days ; but I could 

 not obtain the effect again. I used the same instrument in 

 another investigation during three consecutive weeks, during 

 which various new wires were tried and new combinations em- 

 ployed ; but the effect only came out once more, and this time 

 in the galvanometer. The deflection amounted to about 20 

 divisions of the scale. It lasted for several days and then dis- 

 appeared. 



VII. Relation of unilateral conductivity to previously known 

 phenomena. 



It is perhaps worth while to say a few words about the rela- 

 tion in which the phenomenon described in these pages stands 

 to other phenomena to which a similar name has sometimes been 

 given. Before attempting to do this, however, it is necessary 

 to allude to one or two objections which might be raised against 

 my interpretation of the experiments described above. 



Can the experiments be explained by thermoelectric currents 

 set up by the heating of the wire through the electric vibra- 

 tions ? I think that a careful perusal of the experiments will 

 convince everybody that they cannot be explained that way. I 

 need only draw attention to the unstableness of the effects and 

 to the different facts upon which I thought myself justified in 

 founding the theory mentioned above. These facts certainly 

 cannot be explained by thermoelectric currents. 



At first sight my experiments seem to have some relation to 

 a class of phenomena discovered by Poggendorff"", and described 



* Annalen, vol. xlv. p. 353 (1838), vol. liv. p. 192 (1841). 



