Intelligence and Miscellaneous Articles. 77 



or, developing in a series, 



M=4Ai- E («+ T tJ- 3 * % + • • ■) • • • • ( 2 ) 



a formula in conformity with the preceding measurements. 



Nevertheless the experiment of the dissolution of a magnet is far 

 from simple. Numerous experiments prove that the residual mag- 

 netism of the nucleus is a function of the duration of the more or 

 less rapid dissolution, of the length of the steel, and of a multitude 

 of perturbing circumstances. If the foregoing results suffice to 

 prove the concentration of magnetism at the surface, they cannot 

 serve for finding the exact law of its internal distribution; we 

 shall therefore pursue another course. 



I magnetize the bar after applying to its extremities, upon the 

 two faces, two long armatures of soft iron, tightened by pressure- 

 screws. It is known that it then receives, as if it were infinite, 

 the whole quantity of magnetism which its mean girth can contain. 

 I measure this magnetism, and then, having reduced the bar in 

 aqua regia, repolished its surface at the grindstone, and replaced 

 the armatures, I resume the magnetization and its measurement. 

 I determine, therefore, at each operation thus effected, the sum of 

 magnetism M taken, at saturation, by one and the same steel of in- 

 finite length and diminishing thickness E. 



On the other hand, this quantity of magnetism is expressed by 

 the formula (1). Supposing e=E, we have 



*~nt*-*-^' d^ = o- =constant •• (3) 



For determining the constant h it is sufficient to take upon the 

 curve two values M and M x corresponding to two thicknesses 2E 

 and E: — 



Put l~ E = z , h'^ssz 1 , and, dividing, 



M 



an equation of the second degree, the roots of which are : — the one, 

 z' = l, which does not satisfy the question; the other, 



Taking the millimetre as unit of thickness, the mean value of Jc 

 has been found equal to 1*0853. The following Table shows, in 

 accordance with the formula, that the quotient of M by 1 — 7c -2E is 

 a constant quantity. "We shall, in consequence, admit the law of 

 diminution of magnetism in the interior expressed by formula (3). 



