196 E. von Aubel on the Influence of Magnetism 



The ordinary poles of the electromagnet were replaced by- 

 large flat poles, made of thick iron circular plates, each one 

 having a thickness of 15 millimetres and a diameter of 

 150 millimetres. In this way the magnetic field was made 

 more uniform. 



In order to measure the resistances, Thomson's method 

 was employed, and a Siemens's dead-heat galvanometer, with 

 the magnet in the form of a bell, was used. 



In order to avoid heating the thread of bismuth by the 

 passage of the current, one Grove cell only was used, and, by 

 the aid of a see-saw commutator, the current was not allowed 

 to pass in the bismuth for a longer time than was necessary 

 for the observations. 



The deviations of the galvanometer-mirror were observed 

 in a telescope furnished with a graduated scale, the distance 

 between each division being two millimetres, and placed at a 

 distance of more than seven metres from the mirror. One 

 can judge of the sensitiveness of the method. We have also 

 employed KirchhofFs method of measuring resistances, pre- 

 serving all the other arrangements. A great number of rods 

 of bismuth and its alloys have been tried ; in the following 

 tables we only give the values obtained for a sample of each 

 kind. 



In our experiments we did not obtain directly the re- 

 sistance of the thread of bismuth, because in Thomson's method 

 the wires for conveying the current were not fixed directly to 

 this metal, but to the copper or platinum conductors which 

 served as electrodes. It was necessary therefore to deduct the 

 resistances of these copper or platinum conductors, in order 

 to obtain values relating only to the bismuth. In the case of 

 the wires slowly cooled, we have subtracted the values obtained 

 directly, as the resistance of the platinum conductors exterior 

 to the wire of bismuth, because this latter metal adheres very 

 easily to platinum, and the section of the rod of bismuth 

 is very great when compared with that of the thread of 

 platinum. 



V. Results of Electrical Measurements. 



The values of W are the electrical resistances in Siemens's 

 units ; the values of Wm are the electrical resistances in the 

 same units under the action of a magnet. 



