MAGNETISM. 



tre, was sent out at night in the exact 

 line indicated thereby ; which, being du- 

 ly followed, carried them close to the 

 vessel that was at anchor. Thus the ac- 

 tive power of attraction appeared to be 

 established on both elements, and in the 

 course of time the magnet was fixed to 

 a card, marked with thirty-two points, 

 whereby the mariner's compass was pre- 

 sented to us. The points to which the 

 magnet always turned itself, being gene- 

 rally in correspondence with the meri- 

 dian of the place where it acted, occa- 

 sioned the extremities of the bars to be 

 called poles. Succeeding experiments 

 proved, that the magnetic bar never re- 

 tained an exactly horizontal position ; but 

 that one of its poles invariably formed an 

 angle with any perfect level, over which 

 it was placed : this was not so very mea- 

 surable in a short bar, but in one of a 

 yard in length was found to give several 

 degrees of inclination. This, which is 

 called " The Dip of the Needle," (or 

 magnet) seems to indicate that the at- 

 tracting power is placed within the earth. 

 What that attracting power is we cannot 

 determine ; some consider it to be a fluid, 

 while others conjecture it to be an im- 

 mense mass of load-stone situated some- 

 where about the north pole. The diffi- 

 culty is, however, considerably increased 

 by the known fact of the needles of com- 

 passes not always pointing due north ; 

 but in many places varying greatly from 

 the meridional lines respectively ; and 

 from each other at different times and 

 places. The facility with which a meri- 

 dional line may be drawn by solar obser- 

 vation, and especially by taking an azi- 

 muth, fortunately enables navigators to 

 establish the variation between the true 

 northern direction, and that indicated by 

 the magnet attached to the card of the 

 compass. Nevertheless, we have great 

 reason to believe, that, for want either of 

 accurate knowledge of the prevalent va- 

 riations, or from inattention thereto, ma- 

 ny vessels, of which no tidings were ever 

 heard, have been cast away ; it being ob- 

 vious that a false indication of the north- 

 ern point, in many places amounting 

 to nearly the extent of twenty-five de- 

 grees, must produce so important an er- 

 ror in a vessel's course, as to subject her 

 to destruction on those very shoals, 

 rocks, &c. which the navigator unhappily 

 thinks he steers wide of. To obviate 

 such danger, as far as possible, all modern 

 sea-charts have the variations of the com- 

 pass in their several parts duly noted 

 down ; and in reckoning upon the course 

 steered by compass, an allowance is 



usually made for the difference between 

 the apparent course, by the compass, and 

 the real course, as ascertained by celes- 

 tial observation. Under circumstances so 

 completely contradictory, the principle 

 of magnetism must remain unknown : we 

 know not of any hypothesis which strikes 

 conviction on our minds, or which seems 

 to convey any adequate idea of the ori- 

 gin, or modus operaudi, of this wondrous 

 influence. All we can treat of is the ef- 

 fect; also of the appearances which 

 guide our practice, and of the manner in 

 which the attractive power may be gene- 

 rated and increased. 



In regard to the latter point, namely, 

 the generation and increase of the mag- 

 netic attraction, we shall endeavour to 

 give a brief but distinct view of what re- 

 lates thereto ; observing, that where vol- 

 canic eruptions are frequent, and in those 

 latitudes where the aurora borealis is dis- 

 tinctly seen, the needle or magnet is sen' 

 sibly affected. Previously to earthquakes, 

 as well as during their action, and while 

 the northern lights are in full display, no 

 reliance can be placed on the compass ; 

 of which the card will appear much agi- 

 tated. This has given rise to the opinion 

 held by some, that the power is a fluid : 

 to this, however, there appear so many 

 objections, that we are more disposed to 

 reject than to favour it, although under 

 the necessity of confessing that we are 

 not able to offer one that may account sa- 

 tisfactorily for the various phenomena at- 

 tendant upon magnetism. 



We have already stated, that every 

 magnet has two poles ; that is, one end 

 is called the north, the other the south, 

 pole : the former being considered as ca- 

 pable of attraction ; the other, as we 

 shall infer from the subjoined explana- 

 tions, being far more inert, if at all pos- 

 sessed of an attractive power. When 

 two magnets are brought together with 

 their north poles in contact, they will, in- 

 stead of cohering, be obviously repelled 

 to a distance corresponding with their re- 

 spective powers of attraction, when ap- 

 plied individually to unmagnetised nee- 

 dles. The south poles will, in like man- 

 ner, repel each other ; but the north pole 

 of one, and the south pole of the other, 

 will, when approximated, be evidently at- 

 tracted, and will cohere so as to sustain 

 considerable weights. Iron is the only 

 metal, hitherto known, which is capable 

 of receiving and communicating the mag- 

 netic power; but quiet, and the absence 

 of contact, in some respects, are indis- 

 pensably necessary towards its perfect re- 

 tention. Thus, when a bar has been Ira- 



