MAGNETISM. 



49 



steel tempered at a cherry-red heat, and 

 from twenty to twenty-four inches in 

 length, of rather more than half an inch 

 in breadth, and one-fifth of an inch in 

 thickness. These he first magnetized to 



to each other, and uniting them by their 

 poles of the same denomination, he ar- 

 ranged them into two assemblages, com- 

 posed of five bars in each, separated by 

 small parallelepipeds of soft iron, which 



saturation by means of other magnets projected a little beyond their extremities, 

 procured by any of the methods already and performed the < 



described; then, placing them parallel common to 



Fig. 50. 



office of an armature, 

 the whole set (see fig. 50). 



The moveable part of the apparatus he 

 usually formed of four bars of steel, 

 tempered at the same heat as the pre- 

 ceding, and of the same dimensions as 

 to breadth and thickness, but only six- 

 teen inches long. After magnetizing 

 them as strongly as possible, he united 

 two of them by their widths, and two 

 others by their thicknesses, forming a 

 packet consisting of four magnets placed 

 as close as possible. 



(196.) In proceeding to operate with 

 this apparatus, the large assemblages of 

 magnets, with their armatures, are 

 placed opposite to each other ; so that 

 the magnets which compose them shall 

 lie in the same line, with their north and 

 south poles opposite to each other, but 

 separated by a space nearly equal to 

 the length of the bar to be magnetized, 

 which latter bar is to be laid between 

 the two sets of magnets, resting on the 

 cross bars or armatures, for the space 

 of about the fifth of an inch. Then the 

 moveable magnets are laid upon the 

 centre of the bar, and inclined on each 

 side in opposite directions, so as to farm 

 with each half of the bar an angle of 

 twenty or thirty degrees. 



Every thing being thus prepared, it is 

 at the option of the experimenter to 

 proceed according to the manner of 

 Duhamel, by drawing each packet of the 

 moveable magnets away from the middle 

 of the bar, along that half of it which 

 lies on its own side, as far as the ex- 

 tremity ; or, following the directions of 

 ^Epinus, to retain the magnets in their 

 relative situation, by placing between 

 them a piece of wood or of copper, so as 

 to keep their poles at an invariable dis- 

 tance of one quarter or one fifth of an 

 inch from each other, and preserving 

 their inclinations, to slide them back- 

 wards and forwards from the centre to 

 each extremity of the bar, until each 

 half of Jt shall have been subjected to 



an equal number of frictions. After the 

 last movement has been completed, 

 when the magnets will have been brought 

 back to the centre, where the movement 

 had commenced, they are to be raised 

 perpendicularly to a height sufficient to 

 obviate all sensible disturbance of the 

 magnetic state of the bar, and the ope- 

 ration repeated on its other side. 



(197.) If the pieces which compose 

 the moveable magnets have not previ- 

 ously received all the magnetic power of 

 which they are susceptible, as will gene- 

 rally happen if we have not previously 

 the command of a sufficient apparatus 

 for that purpose, their united power, 

 when assembled in the manner already 

 described, will still produce in the bars 

 subjected to their action in the above 

 process, a degree of magnetism greater 

 than that which they themselves pos- 

 sess. We may therefore avail ourselves 

 of the latter of these bars for composing 

 a new set of magnets, which will accord- 

 ingly be more powerful than the former : 

 and then, obtaining by their means still 

 more highly impregnated magnets, we 

 may again disunite them, and subject 

 them to the action of still more energetic 

 combinations, formed by the bars last 

 impregnated. By the continued repeti- 

 tion of these processes, employing one 

 set of magnetic bars alternately in raising 

 the intensity of those of another set, it is 

 evident that we shall finally succeed in 

 effecting their complete saturation. 



(198.) "When it is required to magne- 

 tize bars of very considerable size, Cou- 

 lomb recommends that the moveable 

 apparatus of magnets should be com- 

 posed of a much greater number of 

 pieces than in the instance above given ; 

 and that these pieces should be disposed 

 in rows, each successive row projecting 

 beyond the last, as shown in Jig. 51 : thus 

 the pole of each, which generally resides 

 at the very extremity of the bar, will 

 E 



