300 Mr. R. H. M. Bosanquet on Electromagnets. 



The linear scale is varied in proportions up to 1 : 5. The 

 largest of the masses weighed considerably over a cwt., and 

 taxed our resources to handle it. 



Dimensions of Bars. 



Plain Bars. 



Bars with solid P.P. (pole-pieces). 



Bars. 



Length, 

 centim. 



Radius, 

 centim. 



n coils. 



Ba rs. 



Length, 

 centim. 



Radius, 

 centim. 



n coils. 



I. 



II. 



IV. 



V. 



VII. 



VIII. 



IX. 



X. 



XL 



XII. 



20 

 20 

 40 

 40 

 60 

 60 

 80 

 80 

 100 

 100 



0-5 

 0-5 

 10 



10 

 1-5 

 15 

 2-0 

 2-0 

 2-5 

 2-5 



1092 

 1109 

 1933 

 1931 

 1951 

 1909 

 2557 

 2543 

 3187 

 3172 



I. 



II. 



III. 



VI. 



XVII. 



XVIII. 



XV. 



XVI. 



XIII. 



XIV. 



206 



20-7 



38-08 



38-08 



57-5 



57'0 



73-9 



73-9 



94-85 



94-8 



0-5 



0-5 



10 



10 



1-5 



1-5 



2-04 



2-04 



2-5025 



2-525 



1121 

 1110 

 2024 

 2134 



2837 

 2813 

 3546 

 3574 

 3041 

 3028 



The determinations of bar II. with pole-pieces were puzzling 

 and anomalous, and were excluded. Determinations for small 

 inductions were in all cases made in the first instance by 

 reversing the effect of the horizontal component of the earth's 

 magnetism. The bars were then wound uniformly from end 

 to end, and the inductions determined by the effect on coils 

 placed equatorially. 



In many cases great discrepancies occurred even between 

 bars of the same measurement (they were all in pairs). In 

 these cases the determinations were repeated, and in several 

 cases the whole of the magnetizing coils were rewound. 



The results were then plotted on a large figure for each bar, 

 and a curve was drawn by hand to represent the values as well 

 as possible ; % was abscissa, and p (magnetic resistance) 

 ordinate. 



It was at once evident that in all cases, almost without ex- 

 ception, the curve did not show p = co for any finite value of 

 3$, but rather indicated the existence of an asymptote inclined 

 at a moderate angle to the axis of/). 



The values of p corresponding to 35 = 0, 1000, 2000, <fcc. 

 were then measured off, and all divided by the lengths of the 

 bars, so as to reduce them to data for bars 1 centim. long, 

 according to the above law r of similarity. 



These values, with the resulting means, form the two fol- 

 lowing Tables, 



