Improvement </fthe Douhle Magnetic Touch, ]}| 



each other, mg^e or lefs according to their force j the points S and S'rcprefenting the 

 fouth, and the points N, N' the north poles. In this fituation the two i)ars were moved 

 from one end to the other of the bar n s. 



M. ^pinus has remarked, that in this method the centre of aftion of the two magnets 

 NS, N'S' being neceflarily placed at fome diftance from their extremities at the point u 

 for example, the a£lion on the points of the bar n s comprehended between the two bars 

 is made very obliquely, and confequently does not communicate as much magnetifra 

 a5 the fubje£l is capable of receiving. Whence, inftead of placing the two bars upright in 

 this operation, M. ^pinus advifes that they (hould be inclined, as in fig. 2 ; and in this 

 pofuion moved from one end of the bar to the other. 



I have, in fa£t, found by the magnetic balance defcribed at the beginning of this me- 

 moir*, that the method of M. ^pinus is preferable to the other; but I have alfo obferved, 

 that it does not give the needles the pcrfe£l faturation of magnetifm, and that frequently 

 when the needle is of confiderable length, feveral poles are formed on the intermediate parts, 

 the action of which is indeed fmall, but neverthelefs perceptible. I attribute thefe to 

 the particular adtion of each magnet, which tends to produce on the points pafled over by 

 the magnets an efFctl contrary to that which is defired. In our figure 2, the pole S for 

 example being placed upon the needle, tends at the fame time to give to the point q, which 

 is placed under the bar, the fame kind of magnetifra as at the point u ; that is to fay, 

 on the hypothefis of two magnctical fluids capable of moving towards the extremities of 

 the needle, if the point u be drawn towards the point n, the point q which is near it will be 

 drawn towards the point s, after this point q fhall have been palled by both magnets. In 

 my hypothefis, in which the magnetic fluid is not capable of moving, except in the inte- 

 grant parts, the molecules u and q, which are near each other, tend to become magnetized 

 in oppofite dire£l;Ions; and mud produce a diminution of magnetifm towards the extremi- 

 ties of the needle, where the magnetic fluid muft be moll condenfed ; a circumftance 

 which may produce feveral poles in very long needles, as Is proved by experience. This 

 obfervatlon, which neceflarily refults from the accurate meafures afforded by my experi- 

 ments, obliged me to depart from the method of M. ^pinus. The following is that 

 which, after various trials, has proved by the magnetic balance to be the moft advantageous. ' 



In my operation I ufe four very flrong magnets impregnated by a firft procefs, which I"" 

 rtiall prefently defcrlbe. I place my two ftrongeft magnets (fig. 3.) NS, NS, on an horizon- ^ 

 tal plane in one right line, at fuch a diftance that they may be a few lines nearer to each 

 other, than the length of the needle n s intended to be magnetized. I afterwards take the 

 two magnets N' S'i and inclining them as in the method of ^pinus, I place them firft on 

 the middle of the needle, or with their poles nearly in contaft. I then draw each magnet, 

 without changing its inclination, to the extremity of the needle, and repeat this operation 

 five or fix times on each face of the needle. It is clear that in this operation the poles of 

 the needle n s remain fixed and invariable at the extremities of the needle, by means of 

 the two ftrong magnets NS on which it refts. The efi^eft produced by thefe can only be 



* The excellent and well known method of Coulomb of meafuring the forces of eleSricity and magnetifm, 

 is by fufpeoding an horizontal lever or bar by a fine wire at the point of fufpenfion ; which bar being turned 

 caufes the wire by its torfion to exert a determinable force againft the afticn intended to be meafured. N. 



Vol. II.— May 179?. M augmented 



