ON THE PERMANENCE OF THE MAGNETISM IN STEEL 



BARS. 



BY S. H. CHRISTIE, ESQ., M.A., F.R.S., &c. 



I 



N the course of some magnetical experiments, made in 

 China, on the deviations of a magnetised needle due to 

 the action of an iron shell, Captain Wilson found, that when 

 the magnetism of the needle was disturbed, by applying the 

 pole of a magnet to the similar pole of the needle, considerable 

 changes were produced in its deviations; and, on Captain 

 Wilson's return to England, the experiments were repeated 

 and extended, and the results classed by Mr. Barlow. These* 

 were considered as quite decisive against a law which I had 

 several years before stated, that the deviations of a magnetised 

 needle, due to the action of iron, followedf. I was, therefore, 

 induced to repeat the experiments ; and having determined the 

 situations of the magnetic centres, the intensity of the mag- 

 netism in different points, and the points of greatest intensity, 

 in needles having their magnetism unequally distributed in 

 their two branches, that is, in which the symmetrical distri- 

 bution of magnetism had been disturbed, which had been 

 omitted to be done in the former experiments, I showed that 

 the results of those experiments were not only consistent with 

 the views which I had previously taken, but were such as I 

 had anticipated from the law referred to J. 



While I was engaged in making these experiments, it became 

 a question with me, how far the deviations of a needle, having 

 its magnetism unequally distributed, observed at the beginning 

 of any set of observations, could be compared with those 

 observed towards the end of the same set, in consequence of 

 a tendency which might exist in the magnetism of the needle 

 to return to a state of symmetrical distribution. My first 

 object was, therefore, to determine whether any change that 

 could influence the results took place in the time occupied in 

 making a set of experiments, an interval of 3 or 4 hours. 



* Plul. Trans. 1827, f Camb. Phil. Trans. 1820; Phil. Trans. 1825. 



1 Phil. Trans. 1828. 



