384 PHILOSOPHICAL tllANSACTIONS. [anNO 16S7. 



netical matter in all the parts thereof analogous to those of the stone. It must 

 only be noted, that in an irregular stone the magnetical virtue appears stronger 

 towards the angles than in the other parts, which may cause some irregularity 

 in this experiment, if it be tried with a stone that is very uneven. 



These experiments gave me the curiosity of making another, by touching two 

 semicircles of steel. Having joined the two ends touched by the same poles, I 

 observed by the steel-dust the same effect as in the ring. But having joined 

 the ends differently touched, I found that immediately the two half rings run 

 together and adhered to each other ; and by the steel-dust strewed on paper, I 

 observed that there were four vortices, one in the middle of each semicircle, 

 and one at each of the places where they joined, and that the two latter were 

 less than the others, and much stronger. I saw likewise that there were four 

 poles, each of which was within a vortex, and that each retained in its semi-* 

 circle the virtue of the ends of the half-rings. 



Having touched a steel wire that was straight, I tried to make a ring of it ; 

 but I found that it had quite lost its virtue, which cannot be attributed to the 

 junction of the poles, since they ought to adhere together, according to the 

 other experiments which have been made ; but only to what has been already 

 noted, that when a magnetical virgula is a little bent, it loses its virtue, which 

 cannot happen but from the alteration in the pores of the steel. 



I further remarked, that a ring of steel touched, for a long time retains its 

 virtue, though it be put in a position contrary to its poles. And this experi- 

 ment is confirmed by another, much more considerable, which is, that a ring 

 of steel, touched with a strong loadstone, cannot without difficulty receive a 

 contrary touch from a magnet less strong than the first ; but that in time by 

 degrees it resumes its former virtue, much as we see magnets do, which being 

 applied to another stone, by the poles of the same denomination, lose their first 

 virtue, and take the contrary ; which they afterwards lose by degrees, to re- 

 assume the first. 



After having presented this new system of the magnet to the Academy, there 

 were made some experiments on a terrella, of much the same diameter with 

 mine, but whose poles were not diametrically opposite; and on a half globe, 

 much larger than the terrella. But no considerable difference or alteration of 

 poles were found in Paris, April 20, 1687. 



This letter having been read before the Royal Society, it was ordered that 

 that the terrella, which has been in their repository these 25 years, the gift of their 

 foyal founder king Charles II. should be examined, to see if there be any sen- 

 sible alteration in its poles : and on trial it was found, that the points which are 

 marked on it with crosses, were as near as could be discerned the true poles of 



