306 Mr. J. P. Joule's Account of Expeiiments 



and 



ACT = 





/*2 (cos2 ^ - sin^ ^/r) (fl« cos^ ^/r + Z»« sin* i/r) 



or 

 . u}ah IT 



fJL O 



Hence in one complete revolution in the oval, or in a double 

 vibration of the pendulum, the progress of the apse-line 



fjJab IT 



But it is evident from the equations for the motion of the pen- 

 dulum, that 



yLt = y (approximately) , 



and 



Hence we arrive at the final result, that the apse-line will make 



S P 

 a complete revolution in time ^ . — r multiplied by the time of 



a double vibration. 



This is the same conclusion as that arrived at by the Astro- 

 nomer Royal in a paper read before the Astronomical Society. 



Believe me, Gentlemen, 



Yours faithfully, 

 Alburgh Rectory, Norfolk, J. A. CooMBE. 



Sept. 24, 1851. 



XLVII. Account of Experiments demonstrating a limit to the 

 Magnetizability of Iron. By J. P. Joule^ F.R,S. 



To the Editors of the Philosophical Magazine and Journal. 

 Gentlemen, 



SEVERAL years ago I published some experiments on electro- 

 magnetic attraction, by which I confirmed the law of Lenz 

 and Jacobi, discovered about the same time, viz. that the mag- 

 netism induced in a soft ii*on bar is proportional to the electro- 

 magnetic force of the exciting coils ; but I was led to the con- 

 clusion that this law fails when very high degrees of magnetiza- 

 tion are attained, and that, indeed, there is a limit beyond which 

 it is impossible to increase the intensity of the magnetic virtue 



