676 PHILOSOPHICAL TRANSACTIONS. fANNO 16Q4. 



should be of which kind I pleased. The terminus, or necessary length for 

 every thickness, increases more than one would think. 



5. Heat a rod, or its end, red-hot, and thoroughly cool this end downwards 

 it will have somewhat more magnetism than if cooled horizontally towards the 

 north. But the better way is to cool it a little inclining towards the north. I 

 cannot find that multiplicity of ignitions produces more magnetism than one 

 good ignition : but it must be thoroughly ignited. Nor can I find by many 

 experiments that quenching in water signifies to the producing or hindering 

 magnetism ; but many ignitions may accidentally promote it by purifying the 

 iron. 



6. Dr. Power says, that if we hold a rod northward, and hammer in that 

 position the north-end, that will become a north pole, i. e. a fixed north pole; 

 contrarily, if you hammer the south end. But this is true only in some cases, 

 viz. it holds in rods only of a certain length : for I say here again, as before of 

 ignitions, that of round bars of the same diameter, there is required a certain 

 Jength, under which a fixed pole cannot be produced by hammering ; but of any 

 length more than that certain length, you may make it; and then if you take 

 a bar shorter than that length of which you cannot make a fixed pole, while you 

 keep that diameter; if you take a rod of the same length but less diameter, you 

 may by blows produce a fixed pole: or if you only beat that thicker bar thinner 

 you may produce a fixed pole, though the rod be never so short, provided you 

 beat it thin enough. 



7. What is said of hammering, is to be understood of filing, grinding, drill- 

 ing, sawing ; or a hard rubbing, or even a soft rubbing, provided it is long, will 

 produce fixed poles; the heavier the blows are, caeteris paribus, the magnetism 

 is the stronger ; I say, caeteris paribus, as when the blows are not so heavy in 

 either case, as to flat the iron, for flatting it produces more magnetism, though 

 other things do not vary. A few hard blows will produce as much magnetism 

 as many, as to sense, as if you give never so many blows; yet a soft blow may 

 produce but little magnetism. The utmost magnetism that I could produce in 

 ordinary rods this way, did not exceed that which an ordinary loadstone would 

 have infused. 



8. Beating many rods northward, whose lengths I knew sufficient, I never 

 failed of produced a fixed north pole ; but hammering the same or like rods 

 southward, I found that I could not produce a fixed south pole, only a mutable 

 pole ; nay, hammering one full south, I produced a fixed north pole ; the rea- 

 son I thought might be, that the hammered south-end on the anvil was a little 

 lower than the end which I held in my hand. I then held the end higher, and 



