76 Intelligence and Miscellaneous Articles. 



It is precisely this state of supersaturation which I have re- 

 garded (I believe, the first) as the general case, governed by a 

 very simple law ; it constitutes the starting-point of my memoir, 

 for the ulterior researches upon the state of permanence. I think 

 it will define the researches of the makers of permanent magnets, 

 by showing them the maximum which can be attained by them. 

 I have sought the empiric formula which connects the portative 

 force of supersaturation with the dimensions of the magnet well 

 forged and tempered, whatever may be its origin. I consider the 

 state of permanence as the special case, variable from one magnet 

 to another, with the origin and with the conditions of making of 

 the steel. Observiug that the maxima of M. Jamin's intensity- 

 curve, which for the state of supersaturation are in the polar 

 planes, spontaneously recede from those planes for the state of 

 permanence, I suspected that there was a connexion between this 

 displacement and the passing from the one state to the other. I 

 measured, for the first state, the distance of these maxima upon 

 the median line — that is to say, the total length I of the horse- 

 shoe taken as a straight bar. Afterwards I measured the distance 

 L of these maxima for the second state upon the median line ; and 

 I have named it the reduced length of the magnet. I then calculated 

 the permanent portative force p by aid of the portative force P of 



supersaturation, multiplying this latter by ( j J 3 ; I thus obtained 



a new empiric formula for_p. 



Calling E the weight of the magnet, and C a constant, Daniel 

 Bernoulli gave the formula ^=CR 3, which he found accurate as 

 long as the magnets compared were of like form. Verified after- 

 wards by Greuns*, Haecker, Elias, and others, this formula has 

 further been found approximately applicable to magnets of different 

 forms ; p and B, beiug given in kilogrammes, the highest value of 

 the constant 0, attained only by the magnets of M. van "Wetteren, 

 is from 21 to 22. My empiric formulae adapted to differences of 

 form are 



p=aovh/4-' CO 



v Vs 

 and 



i-BO^/^-T' cn.) 



in which A and B are coefficients to be determined by experiment, 

 O and s are the circumference and the surface of the polar faces, I 

 and L are the length and the reduced length of the magnet. 



In my memoir will be found the observations which served me in 

 the research of these formulae : — (1) the results found for nineteen 

 simple magnets made by M. van Wetteren with a new steel which 

 he obtains from commerce, the weights of which vary from 0*334 



* Memoire sur les Aimantsf&c, Venlo, 1862. 



