Electrical Resistance of Antimony and Cobalt. 541 



method of measurement employed by me, I will only observe 

 that it was like that of Matthiessen and Hockin, with the 

 exception of some modifications suggested by the special cir- 

 cumstances and object of my investigation. The magnetic 

 field was formed by a large Ruhmkorff electromagnet, ex- 

 cited by a number of Bunsen's elements or by a dynamo 

 machine. 



My experiments on antimony showed that, when brought 

 into a magnetic field, there was an increase in its electrical 

 resistance, both across and along the lines of force. It ap- 

 peared to me moreover that, with the same intensity of the 

 magnetic field, the increase across was greater than that along 

 the lines of force. 



Cobalt I investigated in the form of a small thin plate, pre- 

 pared by electrolysis of the chloride, or by depositing the metal 

 on a plate consisting of a mixture of graphite and stearine, as 

 indicated by M. Bighi*. I soldered two thick copper wires 

 at the two ends of this small plate of cobalt, before detaching 

 it from the plate of graphite and stearine. These wires were 

 rigidly connected by means of a piece of ebonite, and served 

 to make the connexions in the circuit. By a movable support 

 I could very easily adjust the small plate in any position in 

 respect to the lines of force. By a long series of observations 

 I found that : — 



(a) When the plate of cobalt was arranged in the magnetic 

 field with its plane perpendicular to the lines of force, a dimi- 

 nution of its electrical resistance was observed. 



(b) When the plate was arranged parallel to the lines of force, 

 and the current also had the same direction, an increase in its 

 electrical resistance was observed. 



Judging therefore from the intensity of the effects, the 

 behaviour of antimony is the same as that found by M. 

 Bighi for bismuth ; and the behaviour of cobalt the same as 

 that found by Sir W. Thomson for iron and nickel. 



I will not dwell on similar experiments on other substances, 

 because the results are not yet definitive. 



In the meantime I must express my obligations to Prof. 

 Bighi for his encouragement in these experiments, and for 

 also giving me the means of making them in the Physical 

 Institute under his direction. 



Padua, December 12, 1886. 



* Mem. delVAcc. di Bologna, (4) v. 1883, p. 122; N. Cimento, (3) 

 xv. 1884, p. 140. 



