254 Dr. A. Schuster on Unilateral Conductivity. 



went to the other side, and the permanent deflection was nume- 

 rically the same. The same experiment was repeated several 

 times, and the same deflection was always observed. While 

 thinking over this result, I took the apparatus to pieces, i. e, 

 disconnected all wires and joined them again together. The 

 effect had now entirely disappeared, the needle coming to rest 

 exactly at its zero-point. The next day a small unilateral con- 

 ductivity (as the effect may be properly called) was observed, 

 but after a few experiments disappeared again. During several 

 days I found that this unilateral conductivity generally appeared 

 when the wires had had some rest; and I therefore joined into 

 the circuit different wires which had not been used for some 

 time. Some of these wires showed the effect, and some did not; 

 in all cases it disappeared after several experiments. A wire 

 which had never been used before showed the effect in a remark- 

 able degree. The introduction of this wire, which could not 

 have a resistance larger than 0*1 unit, was sufficient to drive 

 the needle wild to one side. I must mention here a remarkable 

 fact. Suppose we have a circuit in its normal state (that is, 

 showing no unilateral conductivity); let us introduce a wire, and 

 suppose that the unilateral conductivity is now observed. Take 

 the wire out again, so that the circuit is exactly the same as it 

 was before when no unilateral conductivity existed. The uni- 

 lateral conductivity will now appear, generally even in the same 

 degree as it did with the new wire. If we now by experimenting 

 destroy the unilateral conductivity and join the wire which had 

 caused the disturbance into the circuit again, it will generally 

 behave quite neutral; i, e. no unilateral conductivity will be ob- 

 served. If it do not behave quite neutral, it will only show a 

 small unilateral conductivity, which will be destroyed by a second 

 or third experiment of the same kind. 



IV. Proposed Theory of the Phenomenon. 



It is chiefly the remarkable fact just described (as well as the 

 previous observation, that generally new wires, or such wires as 

 have not been used for some time, showed the effect) that has 

 led me to a theory which, although proved afterwards to be, if 

 not erroneous, at any rate incomplete, explains so well many of 

 the most startling observations that I think it well to give it 

 here. Supposing we pass an electric spark from a sphere to a 

 point, it is known that the distance the electric spark will pass 

 for a given electromotive force is different according as the sphere 

 is positively or negatively electrified. A circuit composed of a 

 metallic wire, terminated at one end by a sphere, separated by a 

 thin layer of air from the other end of the wire would therefore 

 show unilateral conductivity, the positive electricity passing more 



