76 Intelligence and Miscellaneous Articles. 



to 2*1, diminish regularly down to 0*2; therefore the density of the 

 magnetic layer diminishes from the surface to the centre. 



The fourth column contains the fractions of thickness removed ; 

 the fifth, the fractions of magnetism vanished. These latter are 

 always greater than the former. When the thickness is diminished 

 y 1 ^, the magnetism becomes jV less ; if we take away -i- of the thick- 

 ness, we remove half of the magnetism. In other terms, in consu- 

 ming on each side j 2 ^ of a millim. we take one fourth of the total 

 magnetism, and for 1*1 millim. nearly two thirds. Therefore the 

 two thirds of the magnetism were confined within a layer of 1*1 

 millim. thickness, enveloping a nucleus of 8*4 millims. which pre- 

 serves about one third only of the total magnetism. 



If we remagnetize this nucleus of 8*4 millims., we give it a total 

 magnetism equal to 23*5, nearly as much as the original bar possessed 

 before its wasting. We see that by this remagnetization a new 

 magnetic layer is produced at the surface to replace that which was 

 taken away, and is nearly equal to it, can be itself taken away like 

 the first and be replaced like it in the subjacent thicknesses. 



In steel still more cemented the magnetism intrenches itself within 

 a thickness still less ; but in the commercial kinds of steel, which 

 are much more conductive, the magnetism penetrates almost uni- 

 formly the entire mass, as might be easily foreseen*. 



These results are in harmony with the theory. If it be admitted 

 that, in a bar of thickness 2E, starting from the two faces the mag- 

 netism diminishes according to the same law as in the direction of 

 the length, we find that it is expressed by the formula 



cs is counted from the middle of the bar. To get the total quantity 

 M of magnetism comprised within this bar from — e to +e (that is 

 to say, reduced to the thickness 2e), ydec must be integrated from 

 + c to — e, which gives 



M=?^7c- E Jc e -7r e ); (1) 



* This is the case of MM. Treve and Durassier. They measure the 

 quantity of magnetism by the sine of the delation given by the magnet 

 to a compass near it. All physicists know that this method measures 

 nothing when the compass is close and the deviation great. But if we 

 admit it to be a good method, it will at least require accurate calculation. 

 The quantity of magnetism would be expressed not by the sine, but by the 

 tangent of the deviation, as in the fa;?</e??£-compass. On correcting this 

 error of calculation in the experiments of MM. Treve and Durassier ; it 

 becomes evident that the magnetism is not proportional to the weight of 

 the steel, that it is represented not by a right line, but by a curve, and 

 that the magnetism is denser at the surface than at the centre. In brief, 

 (1) the magnetism is not proportional to the weight of the steel; (2) the 

 method employed was inadequate ; (3) there is an error in the calculation 

 of the experiments ; (4) when it is corrected, results are found conformable 

 to mine. 



