VOL. XVIII.] PHILOSOPHICAL TEANSACTIONS. 677 



SO hammering it south upwards, I never failed producing fixed south poles in 



proper rods. 



g. Old drills and punches are fixed north poles, because almost constantly 

 used downwards : but new drills are either mutable poles, or weak north poles; 

 when I say a new drill, I do not mean one made on the spot, for that is pro- 

 bably a north pole, because quenched downwards in water ; bat then such po- 

 larity made by bare ignition is a weak pole, and soon decays, and turns to a 

 mutable pole : but I mean a drill, which though never or little used, yet has 

 been made some days or weeks; drill with this southward horizontally, and it 

 is a chance if you produce a fixed south pole, but much less if you drill south 

 downwards ; but if you drill south upwards, you may make it a fixed south 

 pole. 



10. The stronger the polarity Is, the longer it will last ; a weak fixed pole 

 may degenerate into a mutable pole in a day's time : yea, I have known it in a 

 few minutes, while exposed to the air, and held in a position contrary to its 

 pole : on the contrary, we find needles touched with good loadstones hold that 

 virtue a great while, if kept from air, and in a meridional position. 



11. The loadstone itself will not make a fixed pole of any iron, only it must 

 have a proper length if it is thick; or if it is short, it must have a sufficient 

 thinness : so, ordinary or weak loadstones cannot fix a pole in a thick short key, 

 which yet they will do in a little key. So in a short thick iron tapering, a load- 

 stone may fix a pole in the little end, when it cannot in the great end. 



12. When ignition, hammering, or a loadstone cannot make fixed poles, it 

 must not be thought that it can do absolutely nothing on such rods, for even 

 then it may be found that there is an effect of magnetism in them discernible 

 enough otherwise, though not enough to make fixed poles. 



13. When you have the due length for making a fixed pole, you will find the 

 making one a fixed north will consequently render the other a fixed south pole ; 

 but if, keeping the same diameter of this rod, you increase its length suffici- 

 ently, the making one end a fixed north pole, will not necessarily make the 

 other a fixed south pole, but leave it a mutable pole. So if you by a like pri- 

 mary operation make the second end a fixed pole, the first end will lose its 

 fixity, and become mutable. There is a certain length suited to every thick- 

 ness of iron, to leave one end mutable, while the other is fixed, and the thicker 

 the iron is, the greater is this length. 



14. If you farther increase the length of the same rotl, you will attain such 

 length, that the oftener you have fixed a pole on one end, and then go to fix 

 the other end, the fixity of the first will not be destroyed, and that end be- 

 come mutable as before, but the fixity of the first end will remain, and so you 



