134 K H. Hall— Effect of Magnetic Force on the 



effect was considerably smaller in the short strip than in the 

 long one, the difference amounting apparently to about 20 per 

 cent. 



Strips differing in Cross-Section. 



Every experiment which bears upon the relation between the 

 transverse action in a strip and the magnetic condition of the 

 strip is of interest. Strips of any strongly magnetic metal 

 under the conditions of these experiments become the more 

 strongly magnetized the greater the ratio of the thickness to 

 the width, but with the non magnetic, or weakly magnetic, 

 metals, no such variation is observable. It is, then, important 

 to ascertain what relation this ratio of thickness to width has 

 upon the transverse action in magnetic and non-magnetic metals. 



Crosses of Norway iron, of cobalt, of nickel, of silver and of 

 bismuth have been tested with this object in view 



Silver. — From a half-dollar coin (silver 9 parts, copper 1 

 part) two crosses were made, the dimensions of which were 

 approximately as follows . 





Width 











Main part. 



Arms. 



Thickness. 



Lengt 





mm. 



mm. 



mm. 



mm. 



No. 1 



9-5 



1-5 



1-02 



25 



Xo. 2 



0-5 



0-5 



1-00 



23 



The smallness of visible effect in these thick pieces of sil- 

 ver made the comparison tedious. The results obtained were 

 nearly as follows, correction being made for the difference in 

 thickness : 



Date. 



Magnetic field. 



Effect in Xo. 1. 



Effect in Xo. 2. 



Feb. 8 or 9. 1886 



9,500 



100 



93 



Feb. 10. 1886 



10.000 



100 



100-9 



July 23, 1886 



10,000 



100 



98-7 



The strength of field is here given roughly in absolute 

 c. g. s. units. The observations of the first day were less 

 accurate and therefore are entitled to less weight than those of 

 Feb. 10th and July 23d. It appears safe to conclude that in 

 the case of silver the "width of the cross has no considerable 

 influence upon the transverse effect. The absolute magnitude 

 of the K. P.* in this metal appeared to be about 750xl0~ 6 . 



*R.P. = £il- T , 



MxC 

 where E represents the total transverse electromotive force in c. g. s. units. 



M represents the intensity of the magnetic field in c. g. s. units. 



C represents the strength of the direct current in c. g. s. units. 



T represents the thickness of the cross in cm. 

 In previous papers I have not given the R. P's in absolute units, having neg- 

 lected, as Professor Boltzmann has surmised {Anzeig. d. Kais Akad.inWien, 1886, 

 Nr. X), to change a resistance from ohms to absolute c. g. s. units. To turn the R. 

 P's given in my article of February. 1885, into absolute c. g. s. units, it is neces- 

 sary to multiply them by 1 9 . 



