184 French National Inft'itute. ; 



flijtd of the bar which a^ on the inagtjetic fluid of ihat poiQt> * 

 is greater than the cohefion which prevents it from being dii- 

 placcd. , . ■ 



But araong all the degrees of mj^j^etifm there is one whi.ch 

 may be caiied the ,poir.L of f;iUiration, or the maximum of 

 marnf.t'fii) ; it is that ,v\here the refult of the forces on eaiOh ^ 

 moiecula is precifely equal to the adhcfiou .ofthal mplepula;, ■ 

 to the Heel. It nay lie readily con'.;>.-.ived that w hen it attains 

 to this llale the ijar his the hichell degree of ma^netifni 

 which it can acquire; it is alfo th~!t degree which. ougbt,);oi,. 

 be given to bars deliined for making, needles to the maimer's., ■ 

 coniiiafs. 



To know whether a needle be magnetized to faturation, prac- 

 tice fecnis 10 furniili bi;t one method, which is,..t.o n^^netize 

 it with Ivirs of difilrent Itrenoth. If a bar, for example, be 

 fuccefliveiy m.igneiized with bars the force of which is- as- • 

 1 to a, and if tlic !);>r tlie firft-lime h-;*; the fame dirot'-iite force 

 a' when magnetized with the lirongeft magnet!*, it appears 

 that we may thence conclude, with a great de;-! qf proba- 

 bility, that the bar is magnetized to fill urri.; ion. Theory fur- , 

 r.ifhes ug with a more direft method, which- is, to find by 

 C'dculalion wdiat may be the di;e6tiiTg. force of a bar tviaiff- . 

 Dctized to liituration, and to exannnc wheth-er the refult of 

 this calculatien be agreeable 10 experience. It -was in this 

 manner that Coulomb proved, in tlie third' volume, of the , 

 Memoris of the Inftiuite, p. 176, that if two bars of ftcej'^ 

 all the tides ot which are homoh>gous, that is to fay, the cor- • 

 refponding iHi^-'S of .vhirh are in ihc fame ratio, be compared 

 with each other, thefo bars, fufpeudcd horizoniaVly as the > 

 needles of a com pal's, .'.ill have the momenta of il>eif d<re<Sl-. . 

 ing forces as the cube of one of their dimenfioivs. . Thisr^i- 

 fnk perrecliy aiuees with what lias, been foi^.nd Uy expert- • 

 ment; vh.:h aflbrd:, a new confirmation of the theory.: 



In thepiefent mi-moir the author endeavours to determine 

 the magiie'iic flate of feveral bars united in .fuccefiion one 

 above ;he other, or, what ainnimts to the fame thi;ig, to de- 

 termine the force of d:ife"nt bars in rcgar^l to their tlu jknefs. 



but it may be calily conceived that, if the theory adopted 

 is agreeable to nature, when' two bsrs of great breadth, and 

 very tiun, are magnetl.(ied to i'jturation, each po/ijU magnet- , 

 ized, in the two bars united, will experience, .011 the part of • 

 thefe two b^rs, an a6lion almofl: double to that which the ,- 

 fame point .vould experience if each bar magn< tized.lo, fatu- . 

 ration were infulated. Thus, by imiting the' two bars, each 

 of them ought to retain only a little more thi^n half the mag- . 

 nctifin which it );ad when infulated, fmce the adheiion is 



the 



