104 



HENRY A. EOWLAND 



? m 1***-i), 



f \ (jf + ti / 



or, to a greater degree of approximation, 



r" 



+ 1-6 



(9ft) 



Before applying these formulae to any series of observations, the 

 latter should be freed from most of the irregularities due to accidental 

 causes. For this purpose the following Tables have been plotted and a 

 regular curve drawn to represent as nearly as possible the observations; 

 in other cases a column of differences was formed and plotted. In 

 either case the ordinates of the curves were accepted as the true quan- 

 tities. But, for fear that some might accuse me of tampering with my 

 observations, I have in all cases added these as they were obtained. 



TABLE IV. 

 BAR -19 INCH DIAMETER. AT CENTRE OF BAR. 



The correction is necessary, because small irregularities in the obser- 

 vations will produce immense changes in r 2 . 



Table IV contains some of the best observations I have obtained. 

 It is from a bar 57 inches long with a helix 1| inch long in the centre 

 to magnetize it. Each quantity is the mean of six observations, these 

 being made on both ends of the bar and with the current in opposite 

 directions. 



In this Table a source of error was guarded against which I have not 



