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which we call gravitation, its operations are not confined to the 

 surface of our globe, but must extend to the whole solar system ; 

 and if all space is filled with the magnetic fluids of the different 

 celestial bodies according to their respective magnitudes, their 

 movements must be explained differently to the commonly re- 

 ceived hypothesis ; because a resisting medium is incompatible 

 with the Newtonian philosophy, and a perfect void is indispen- 

 sable to the assumed geometrical movements demonstrated in 

 the i Principia/ 



CHAPTER XVII. 



UNIVERSAL MAGNETISM. 



With regard to the absolute diameter of the terrestrial mag- 

 netic fluid, there is no definite data by which we can ascertain 

 it ; but from the apparent influence of the moon on the surface 

 of the earth, together with her orbitual motion round the globe, 

 we have reason to suppose that it extends to the orbit of the 

 moon. Within the tropics we have striking evidences of the 

 influence the changes of the moon have on the growth of vege- 

 tation. From the new moon to the full there is a very intense 

 action of the sap, accompanied by a great evolution of hydrogen 

 from the leaves ; and so strongly saturated are the trees during 

 these periods throughout the year, that if cut and used for any 

 purpose they would become rotten and useless in the course of 

 a very few months. During the latter period of the change, 

 viz. from the full to the new moon, there is a temporary sus- 

 pension in the action of the sap, the woody substance becomes 

 consolidated and is rendered fit for cutting. So much is this 

 the case, that we find it rigidly attended to, from the making of 

 a common fence to that of the largest works. It does not 

 folio w r , that if a tree should contain 100 rings that it is a hundred 

 years old ; because within the tropics there are monthly rings, 

 formed by the expansion of the external part of the trunk 

 during the rise of the sap, and not, as has been supposed, by a 

 mechanical return of the superfluous sap from the branches 

 downwards between the trunk and the bark. A bamboo of three 



