130 M E M O I R S 19/ the 
bare ignition 5 and there is no rod, ever fo fhort, but which, ff 
you nnake it fufficiently thin, is capable of a fixed pole^ the 
neceflary length, for every thickneis, increafes more than one 
would think. Heat a rod, or its end, red hot, and thoroughly 
cool this end downwards, or towards the Nddir, it will have 
Ibmething nnore of magnetifm than if cooled horizontally towards 
the north , but the better way is to cool it, a little inclining to- 
wards the north ; repeated ignitions do not produce more magne- 
tilm than one good ignition, but it mud be thoroughly heated 5 
nor does quenching in water contribute to the producing or hin- 
tlering maj;nctiliTJ5 but many ignitions m.ay accidentally promote 
it, by puritying the iron. Dr. 'Poiver lays, that if a rod is held 
northwards, and the north end is hammered in that pofition, it 
will become a north pole, /'. e. a fixed north pole - contrarily, if 
you hammer the fouth end ^ but this is true, as we faid before 
of ignitions, only in rods of a certain length and thickneis. 
What is faid of Hammering is to be underftood of filing, grind- 
ing, drilling, fawing, even a foft rubbing, providing it be done for 
ibme time, will produce fixed poles 5 the heavier the blows are, 
c^eteris paril^uSy the magnetifm is the greater 5 I fay, ceteris 
f^ribiiSy as when the blows are not fo heavy in either cafe as to 
flat the iron, for flatting it produces more magnetifm, tho' other 
things do not vary 5 a few hard blows will produce as much mag- 
netilrn as many, yet a foft blow may caule but little magnetifm 5 
the utmoft magnetifm produced this way, did not exceed what 
an ordinary magnet would have communicated. Striking many 
rods of proper lengths northwards, a fixed north pole never failed 
to be produced; but hammering the fame, or like rods, Ibuth- 
wards, no fixed Ibuth ,pole could be produced, only a mutable 
pole; nay, hammering one full fouth, the author produced a 
fixed north pole, which he thought might be owing to this, that 
the hammered Ibuth end on the anvil was a little lower than the 
end he held in his hand; then he held the end higher, and {o 
hammering it f )uthwards, he never failed producing fixed ibuth 
poles in proper rods. Old drills and punches are fixed north 
poles^ becaule almoli conftantly ufed downwards. The flrongcr 
the polarity is, the longer it will lait ; a weak fixed pole may 
degenerate into a mutable pole in a day's time ; on the contrary, 
needles, touched with good loadflones, hold that virtue a 
great while, if kept from air, and in a meridian fite. The 
ioaddone itfelf will not make a fixed pole of any iron; it 
muO- have a proper length if it is thick; or if it is ihort, 
;t mull: have a fufficienc thinnefs; fo ordinary or v;eak load- 
ftoncs 
