upon the Magnetic Needle. 20') 



ccptible of decomposing water on the appioacli of two wires 

 hianchiiig from the poles of the pile. This phitnomejiou, which 

 I believe was already known, is easily to be conceived, and is 

 equally produced with needles of steel not magnetised, of silver, 

 of platina, &c. 



Notwithstanding the feeble magnetism of this small needle, 

 when put out of the magnetic meridian it recovered it promptly 

 enough. It ])resented the same phaenomena of declination as 

 the needle to the pivot, and that without sensible oscillations. 

 But I have further observed, that when the conducting wire was 

 horizontal, and in the magnetic meridian of the needle, the latter 

 turned round its middle point, which remained fixed ; which suj)- 

 poses a certain symmetry of effects, and appears to nie to lead, 

 besides, to the consequence, that, in that case, the existing forces 

 decomposed, according to the plane of the nnfaccof the water, are 

 reduced to two eijuals, opposite to and equally removed from the 

 middle point of the needle. 



It remains to me now to describe the movements of this 

 needle according to the magnetic meridian. I have formed a 

 table of them. For the sake of brevity, I designated the direc- 

 tion of the conducting wire by always commencing at the ex- 

 tremity of that wire by which it approximates to the zinc p<i1l 

 of the pile. The indication of movements applies equally to the 

 two poles of the needle, and they may be indefinitely i)rolonged 

 on the surface of the water*. The expressions of attradicm or 

 refjulsion indicate that the needle approximates or recedes from 

 the conducting wire. 



-Above the surface of thel From east to west f — repulsion. 



water and directed J From west to east — attraction. 

 [Under the needle (in the\ From east to west — attraction. 



water) and directed J^From west to east — repulsion. 



To the east of the needle \ Downwards — attraction, 

 and directed j Upwards — repulsion. 



To the west of the needle \ Downwards — repulsion. 

 V and directed J Upwards — attraction. 



When the conducting wire is quite perpendicular to the meri- 

 dian plane, the movement of the needle has constantly taken 

 place according to the magnetic meridian |, which rc(|Mires tliat 

 the forces then existing, decomposed according to the plane of 

 the surface of the water, should give a resulting direction cor- 

 responding with the magnetic meridian. If moreover the mid- 



• The water was distilled, in order to lessen the decomposing action of 

 the pile. \ These directions are tilwiiys j^iven aeeordinir to the needle 



of the compas!). J In the contrary case the movement is involved with' 



that of the dedlnution, 



die 



