36 | Hints for the Formation of 
the fouth, at different diftances from the poles of the earthy 
which perform their revolutions in different times; and that, — 
from the combined influence of thefe two poles, we may 
conclude the annual changes of the declination with fo much 
precifion, that we can deduce the longitude of any place from 
its latitude, and wei the degree of foci ein which the 
needle experiences * 
5. Thus, by fappaliig one or more magnets in the inte- 
rior part of the earth, the annual changes of the declination 
and inclination may be explained by the rotary movements 
of thefe magnets. But in the fyftem, which does not admit 
thefe internal magnets, it is afked, Whether the changes of 
declination might not depend on movements which produce 
the change of obliquity, preceffion, nutation, and perhaps 
other phenomena or inequalities of that kind t. 
6. With regard to diurnal variations, an Englifh philo- 
fopher, Mr. Canton, confidering that it is proved by expe- 
rience that heat diminifhes the force of the magnet, thought 
that the folar rays, by heating the earth, muft leffen the at- 
tractive force of the grand magnet contained in it; and he 
thence deduced, as will be feen hereafter, an explanation of 
thefe variations. But Mr. Canton did not reflect on what 
* Heads of Leétures by S. Prieftley, London 1794. 
+ iEpinus gives another explanation independent of thefe movements. 
It may be poffible, according to this philofopher, that the declination of 
the magnetic needle arifes, in general, from the irregular figure of the 
nucleus of the magnetic globe,.or from an unequal diftribution of the 
fluid’in its interior part ; and to account for the variation of this declina- 
tion in one place, in the courfe of time we might fuppofe that the figure 
of the nucleus, or the diftribution of the fluid it contains, is itfelf vari- 
able. /Epinus prefumes alfo, that the action of the iron-mines difperfed 
throughout the bofom of the globe, may have an influence on the varia- 
tion in queftion; and may, perhaps, be the fole caufe of it, Tentamen 
sbeoriae eledir. et magnet. p. 268, 271, 334- 
This philofopher withes that men of fcience, who have an opportunity 
of being near a mine of loadftone, w ould determine, by obfervation, whe- 
ther the maffés of this mineral, before th vey are taken fom the bowels of 
the earth, have their poles difpofed, in regard to the poles of the world, 
hike thofe cf needles freely fufpended: and whether, in certain maffes, the 
poles are not in an inverfe dire€tion, of which he fhews the poffibility by” 
means of confequent points. Lid. p. 333.—Note of the fame. 
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