INFLUENCE OF THE SUN AND MOON. 419 



If these stars are magnetised like the Earth, the greatest variation 

 which they could produce at the equator, on the declination, is less 



lo- 6 i" 



therefore than or , that is to say, absolutely inappreciable. 



4 20 



To have variations of 10', such as are frequently met with, the 

 intensity of the magnetisation of the Sun and of the Moon, must be 

 12,000 times as great as that of the Earth. Now the most powerfully 

 magnetised steel has not 10,000 times the intensity of the Earth; 

 hence, to produce a deviation of 10', the Sun and Moon should be 

 more powerfully magnetised than the best steel magnets. 



The same conclusions result from supposing that the Moon, for 

 instance, is magnetised by the Earth. If the Moon is at the equator, 

 the action which it experiences from the Earth is 



and the value of the intensity of the magnetisation is 



From this is deduced 



r 



t*v m i w (*: 



\D) 5 W 



Whatever value we assume for the coefficient k if even we 

 compare the Moon with the very softest iron the ratio of the 

 magnetisations will be always very small, and the reaction of the 

 Moon upon the Earth may be completely neglected. Still more 

 must this be the case with the Sun. 



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