( 414 ) 



For an investigation of the variation in different magnetic fields 

 the observations are not accurate enough ; yet they already show 

 that the increase is more rapid than proportional to the first power 

 of the magnetic force, but not so rapid as proportional to the second 

 power '). 



b. Results of other observers. 



As far as I know it is only Leduc ^), the discoverer, and voN 

 Ettingshausen 3), who have observed this phenomenon. 



From the former's observations follows for 3/ = 7800 - = 1,057. 



9 



VON Ettingshausen finds numbers varying from 1,052 to 1,021 

 in a field of about 9000. 



In both these cases the bismuth was directly soldered to the 

 source of heat, and for the calculation use was made of the term 

 p e— "^ only. As my value, 1,058 in the field 6000 is rather too 

 large than too small, we can deduce with certainty from the obser- 

 vations that this change is considerably smaller than of the elec- 

 trical conductivity. 



5. Loiiyltudlnal thermo-magnetic phenomenon. 



a. Measurements. This phenomenon may be considered as an 

 increase of the thermo-electric power of bismuth in the magnetic 

 field. I therefore wished to measure the variation of the deflection, 

 observed with the galvanometer, when the copper wires of the thermo- 

 electric couples were connected to it, in percentage values for diffe- 

 rent magnetic fields, always with both directions of the magnetic 

 field, in order to avoid the disturbances caused by tranverse pheno- 

 mena ; afterwards it would only be necessary to determine the thermo- 

 electric power outside the magnetic field once for all, in order to 

 be able to express the longitudinal effect also in absolute measure. 

 Now it was also desirable to make these measurements with the 

 thermo-elements at the places B and C; but as the temperatures of 

 these places vary on applying the magnetic field, a disturbance arises 

 which reduces the change in the deflection, because the fall oftem- 



') A variation of ff with temperature, outside or iu tlie magnetic field, oug-ht to 

 appear from a similar change in A: It is evident that the accuracy of the observa- 

 tions is not sufficient to draw from them conclusions as to such a variation ; how- 

 ever the variation cannot be very large. 



-) C. 11. 104, p. 17S3, 1887. 



'■' Wied. Ann. 33, p. 139, 1888. 



