258 PHILOSOPHICAL TRANSACTIONS. [aNxNO 1705. 



nor could any thing be recovered by shaking, but only the bright sparks, as 

 at first. 



Account of some Magnetical Experiments and Observations. By W. Derham 

 Rector of Upminsler in Essex, and F. R. S. N° 303, p. 2 1 36. 



Having lately invented an azimuth-compass, as I was preparing it for ob- 

 serving the magnetic variation, I took occasion to try several magnetic experi- 

 ments ; and by that means met with this odd phenomenon. Having touched 

 a piece of wire, so that it tended strongly N. and S., I had a mind to see 

 whether it would have any inclination to either of the poles of the world, when 

 turned round like a ring, so as that the two ends of the wire met. And having 

 again straightened it, I was surprised to find it had quite lost its verticity. The 

 cause of which I presently concluded to be the contact of the northern and 

 southern ends of the wire, which I thought might so influence each other, as 

 to confuse its poles ; although I confess I had never observed any such con- 

 fusion to arise from the bare contact of the northern and southern ends of two 

 other touched pieces of wire. 



On this I touched strongly the same, and other pieces of fresh iron wire, and 

 having found them all to turn eagerly N. and S. I coiled them round so as that 

 the ends should not come near each other, and again speedily opened them 

 straight ; and found, as before, that every piece had utterly lost its verticity : 

 nay, the magnetic virtue was so absolutely destroyed by bending the wire, that 

 it had not only lost its inclination to either pole, but the two ends of each wire 

 seemed indifferent to the poles of the loadstone, viz. whereas, before the bend- 

 ing, the adverse poles of the loadstone would repel, and the similar poles at- 

 tract the adverse, or similar ends of the wire ; now the repulsive virtue was 

 quite extinguished, and either end would indifferently be attracted by either 

 pole of the magnet ; just as if the wire had been heated red hot (which is well 

 known to destroy the virtue) or never had been touched at all. 



This I repeatedly experimented on wires of different lengths, with the same 

 success. Only this must be observed, if you only bend the wire round in such 

 a manner that it shall spring back into its place, or recoil, so as to be near the 

 same straightness, that then no such, or but little of such effect, will ensue. 

 But to produce this effect, the wire must be sharply bent, so as that violence 

 may be exerted on it. If it be coiled two or three times round a small round 

 stick, it will succeed best. It is also necessary that every part of the wire be 

 bent, to evacuate the magnetic virtue ; for if the ends, or any other part hap- 

 pen not to suffer the violence of bending, that part will retain its magnetism. 

 As for instance, if the wire be all coiled, except half an inch, or indeed half a 



