Magnetism. 29 



and, indeed, in different parts of the day. Mr. 

 Gilpin found by a mean of twelve years, from 

 1793 to 1805, that the declination" appeared to 

 increase, or go westward, from the winter solstice 

 to the vernal equinox O'.SO ; to diminish, or go 

 eastward, from the vernal equinox to the summer 

 solstice 1'.43; to increase again, from the summer 

 solstice to the autumnal equinox, 2'. 43 ; and to 

 decrease only OM4 from thence to the winter 

 solstice. These minute changes were observed to 

 take place at London : corresponding mutations 

 have been noticed in different parts of the conti- 

 nent of Europe. 



With regard to the diurnal variation, Colonel 

 Beaufoy, whose observations have been carried on 

 for some years, at Bushey-heath, near Stanmore, 

 finds the maximum variation to occur at about 

 half an hour past one o'clock in the afternoon. 

 The mean of his observations for May, 1819, 

 give, at 8h. 37m. A. M. 24 32' 42" W. 

 at 1 h. 24 m. P. M. 24 41' 22", 

 at 7h. 26m. P.M. 24 34' 10''. 



The mean for June, 1819, 



give, at 8h. 40 m. A. M. 24 31' 28" W. 

 at Ih. 29m. P.M. 24 41' 41". 

 at 7h. 47 ra. P. M. 24 35' 09". 

 No satisfactory theory of these variations has 

 yet been adduced. 



Magnets, while they attract other bodies, appear 

 to be themselves subject to the attraction of the 



