Prof. E. Bouty's Studies on Magnetism. 189 



points characteristic of the end fragments and of the entire 

 needle will fall of themselves on the curve. If this condition is 

 not satisfied, the experiment will be rejected. 



Experiment shows that different fragments of the same needle 

 broken before magnetization, magnetized separately to satura- 

 tion, give points that place themselves on the curve traced fro :i 

 the breaking of one of them (the longest, for instance). This 

 important experiment proves that in the present case the break- 

 ing has really no effect at all. 



Equation (1) represents a curve tangent to the axis of a? at the 

 origin, and an asymptote to the right line 



y=A*»(*-|) (2) 



The curves representing the experiments present the same general 

 characters. To make the comparison, the asymptote of the ex- 

 perimental curve is determined with the utmost care. In fact, 

 starting from a length of from 10 to 40 centims. according to 

 the diameter, the points characteristic of the needles fall rigo- 

 rously in a right line, or only deviate within the limits of errors 

 of experiment ; the asymptote is therefore perfectly determined. 

 Let J) be its abscissa at the origin, C its angular coefficient ; the 

 equation can be put in the form 



y = c(*-D ^*-*~^ ) (1/) 



This formula has served for calculating the magnetic moment of 

 short needles ; the real moment is determined directly upon the 

 experimental curve. 



It is in this way that the following Tables have been formed. 

 The first column contains the lengths of the needles ; the second, 

 the observed magnetic moments in arbitrary units; the third, 

 the moments calculated by the formula (1'); the last two, the 

 absolute and relative differences of the observed from the calcu- 

 lated moment. 



The experiments were made on needles of 0*175, 0*282, 0*368, 

 and 0*551 millim. diameter. We will confine ourselves to the 

 results furnished by the last three, because the representative 

 curve of the first is too near a right line, for all lengths above 2 

 millims., for any certain conclusions to be deduced relative to 

 the part of the curve in the vicinity of the origin. 



