52 Dr. A. Stoletow on the Magnetizing -Function of 



roll and tbe magnet, as well as on the distribution of the mag- 

 netism in the latter. 



From the dimensions of the roll and the numbers of the con- 

 volutions of its four layers of wire, there was found 

 F= 6075500 sq. millims. 



The second constant /3 could now be ascertained by experiment. 

 To that end the angles of deflection u x and « 2 of the magnet 

 were observed, which were occasioned by the roll when, traversed 

 by a constant current, it was placed at two different distances r x 

 and r 2 . Then evidently * 



tan w, 



i 



/3= 



tana 2 \r,/ t ? ,2 > 



tan u x (T£\. 



tanw 2 XrJ 



T 



In this determination, the most advantageous ratio — is found 



by the rules of the calculation of probabilities to be = 1336. 

 Accordingly with r x = 1000 millims. r 2 was taken as = 1335 

 millims. In this way I obtained /3= —26301, and therefore 



HtanM =0-011831 for r==10 00 millims., 



= 0-0061169 for r=1250 „ 



The absolute intensity of the current can be calculated accord- 

 ing to these formulae, provided that the quantity H is known. 

 This was measured thrice in the course of the investigation, by 

 Gauss's method. In order to take account of the variations of 

 H in the intervals, the deflection-bar used in the measurement of 

 H was daily placed upon the board which carried the roll, at the 

 distance of 1250 millims. from the latter, and the deflection of 

 the suspended magnet was observed ; from this the alteration of 

 H since the last measurement could be ascertained. It is true 

 that the magnetic moment of the bar was not altogether con- 

 stant ; the variation, however, was caused chiefly, perhaps, by 

 the temperature, and could still be allowed for. I will now call 

 attention to some sources of error in the method described. If 

 we so form the secondary closing that the number of effective 

 turns is =0, small deflections of the magnet are to be expected, 

 even independently of the unhomogeneousness of the iron and 

 of the primary convolutions, as soon as the position of the com- 

 mutator Cj is changed. These arise partly from the interrup- 

 tion of the primary current, but partly from the extra currents 

 which are induced in the primary wire of the ring as well as in 

 the roll. The first and third of these disturbances act, as may 



