494 



Mr. S. Bidwell. On the Lifting Power of [June 10, 



appear as absolutely straight if they were prolonged indefinitely. 

 Assuming the curve of W" to be really straight, the curve of | is 



represented by 



&P +ii=(5-3f+1280%, 

 2^-12800 g + g=5% 



i 



Hence for an infinite magnetic force 



|=5%=5200 C.G.S. units. 



The curve is a hyperbola, an asymptote of which is parallel to the 

 axis of J. 



Similarly, if we assume the curve of j to be a straight line, the 

 curve of W must be a parabola. From the experimental results it is 

 impossible to determine whether either curve is in fact a perfectly 

 straight line. But in neither case do they give any evidence of the 

 existence of a limit, and if there is one it must be very much higher 

 than it is generally believed to be. 



The third column of Table II shows the values of the coefficient 

 of magnetisation or the susceptibility, k (derived from J=/cp), which 

 correspond to different values of J. 



If Jjj denote the magnetic induction and /i the magnetic perme- 

 ability — 



and fi=\-\-4i7rK. 



We can, therefore, easily find the values of g and corresponding 

 with different values of J. These values are given in the fourth and 

 fifth columns of Table II. 



In connexion with the well-known experiments and views of 

 Professor Rowland, the figures thus obtained are of the highest 

 interest. In order to exhibit the results of his experiments in the 

 form of a curve which (as he believed) would be of finite dimensions, 

 Rowland adopted the method of plotting the values of ft as ordinates 

 against those of J as abscissae, and thus obtained the curve shown by 

 a dotted line in fig. 2, which is taken from his paper. The curve was 

 carried by actual experiment as far as the point marked X, before 

 reaching which it had apparently become an almost perfectly straight 

 line. Rowland, therefore, assumed that the line would continue to 

 be straight until it met the horizontal axis at a point C, the abscissa 

 of which would indicate the greatest possible value of § for an 

 infinite magnetic force. He thus arrived at the conclusion that for 

 ordinary bar iron the maximum of magnetic induction was about 



