500 



Mr. R. H. M. Bosanquet on 

 Table III. 



2 q 2 

 C 2 = O Ci. 



e. 



Induction. 



Diff. 



90° 



•0000 





80 



•0752 



•0752 



70 



•1508 



•0756 



60 



•2268 



•0760 



50 



•3025 



•0757 



40 



•3769 



•0744 



30 



■4479 



•0710 



20 



•5099 



•0620 



10 



•5532 



•0433 







•5695 



•0163 



The numbers in the column headed Induction are the 

 values of 



iQiW + 3^J(-3)Q 3 W + ^6 JJ('3) 2 Q 3 W+ • • • 



The last two entries are liable to a small error from omission 

 of Q 9 &c. 



LVIII. Permanent Magnets. — III. On Magnetic Decay (con- 

 tinued). By R. H. M. Bosanquet, St. John's College, 

 Oxford. 

 To the Editors of the Philosophical Magazine and Journal. 



Gentlemen, 



IN the Philosophical Magazine, ser. 5, xix. 1885, pp. 57-59, 

 I gave an account of the decay of the magnetism of a 

 pair of permanent magnets during some months after they 

 were made. 



Observations for H have been continued at intervals with 

 the same pair of magnets, both in the laboratory and the non- 

 magnetic room ; incidentally a large number of determinations 

 of the moments of these magnets have been obtained, and from 

 these an interesting result appears to follow with considerable 

 certainty. 



The decay of the magnetism proceeds much more rapidly 

 in summer than in winter ; and in all probability the rate of 

 decay is quicker for higher temperatures and slower for lower 

 temperatures. 



It will be remembered that Joule proved, by burying 

 systems of magnets for several years, that the maintenance of 

 a constant temperature did not secure the constancy of the 

 magnetic intensity (Reprint, vol. i. page 51)2), on which Joule 



