Dr. A. Schuster on Unilateral Conductivity. 257 



by him under the name of bilateral deflection {doppelsinnige 

 Ablenkung). It seems that the currents in alternate direction 

 affect to a certain degree the temporary magnetization of the 

 needle. This has of course an influence on the time of vibra- 

 tion, which is shorter while the current increasing the mag- 

 netism passes through the galvanometer. While the current 

 passes in this direction the needle makes a greater way than in 

 the same time while the current in the opposite direction is 

 passing. The two currents succeeding each other at regular 

 intervals of time will therefore not counterbalance each other, 

 but the current increasing the magnetism of the needle will have 

 the upper hand. 



The result will be that the needle will be driven towards the 

 side to which it was originally deflected. This, of course, only 

 happens if the effect of this magnetization is sufficiently strong 

 — that is to say, if the original deflection is sufficiently large ; 

 for the magnetizing effect on a needle, placed at right angles to 

 the axis of the galvanometer-coil, is zero, and increases as the 

 sine of the angle of deflection. According to Poggendorff, 

 a needle which is not deflected more than eight or ten degrees 

 from its zero-point, will return to that point if currents in alter- 

 nate directions are sent through the galvanometer. If, how- 

 ever, the original deflection is greater than 10 degrees, the 

 needle is driven violently towards the side of this deflection. 



It is evident that this effect of the electric vibrations is a 

 function merely of the position of the needle ; altering the con- 

 nexions could therefore never produce a reversal of the effect. 

 As, however, I could always drive the needle towards the other 

 side by suitably changing the connexions, this bilateral deflec- 

 tion has evidently had nothing to do with the above experi- 

 ments. 



It remains to say a few words about what has been called 

 unipolar conductivity. This unipolar conductivity has been ob- 

 served in electrolysis and in flames. The unipolar conductivity 

 in electrolytes has been explained by secondary influences of 

 electrolysis*, and, therefore, does not stand in any relation to 

 what I have called unilateral conductivity. The unipolar conduc- 

 tivity of flames lias not yet been satisfactorily explained. If my 

 supposition is correct, and if we must look to the air condensed 

 on the surface of the wires for the explanation of unilateral con- 

 ductivity, it will most likely prove to be closely allied to the 

 unipolar conductivity of flames. 



VIII. Conclusion. 



The result of the foregoing investigation may be perhaps best 

 stated as follows : — 



Phil Mag. S. 4. Vol. 48. No. 318, Oct. 1874. S 



