Dr. A. Schuster on Unilateral Conductivity. 253 



rausch and Nippoldt in a research on the conductivity of sulphuric 

 acid*. I take the following data from the latter paper. The 

 resistance of the wire wound round the magnet is 30 mercury 

 units f. The mean electromotive force of the induction-shocks is 



^-77 Grove in each direction if the magnet rotates n times in a 



342 



second. During the following investigation the magnet rotated 



about forty times a second ; so that the resultant electromotive 



force in each direction was about 0*12 Grove. 



The resistance of the galvanometer was found to be about 

 2477 mercury units ; so that the resistance of the whole circuit 

 was as nearly as possible 2500 units. The galvanometer had a 

 plane mirror, and was read off by means of a telescope and scale 

 at a distance. In order to have an idea of the delicacy of the 

 instrument, I measured the deflection produced by a known 

 electromotive force, and I found that the electromotive force of 

 3 1 Daniell caused a first deflection of 200*4 divisions of the 

 scale. The whole arrangement is therefore extremely simple, 

 and is represented by the following diagram : — 



© 



1? 



G is the galvanometer, I a coil of wires within which the rota- 

 ting magnet is placed. 



III. Description of Experiments. 



When I first joined the galvanometer to the inductor and ro- 

 tated the magnet, the effect on the galvanometer-needle was such 

 that I was afraid of a bad contact either in the galvanometer or 

 in the inductor. The needle started wild to one side, then 

 suddenly stopped, turned back to the opposite side, and moved 

 from one side to another without any law. The only regularity 

 I could perceive was that it started always in the same direction. 

 On changing the wires leading to the galvanometer, the needle 

 invariably started to the opposite direction. I broke the con- 

 nexions and left for about two hours. When I came back every 

 thing had changed. On working the siren the needle now went 

 slowly to one side, and after a few oscillations came to rest at a 

 point about ninety divisions of the scale from the zero-point. 

 On changing the wires leading to the galvanometer the needle 



* " On the Validity of Ohm's law for electrolytes, and a numeric deter- 

 mination of the conductivity of sulphuric acid/" Pogff. Ann. vol. cxxxviii. 

 p. 379 (1869). 



t All resistances in this research are referred to mercury units. 



