1864.] 439 [Chase. 



Gen. Sabine's magnetic " decennial period," and Scbwabe's period 

 of solar spots. 



The law of varying attraction suggests a plausible explanation for 

 the approximate mean proportionality of the barometric to the tidal 

 and magnetic variations. For the ratios of attraction of any planet 

 when in solar conjunction, at quadrature, and in opposition, vary as 

 (n +1)^, n2, and (n — 1)'~, respectively, the attraction at the 

 mean distance being nearly a mean proportional between the maxi- 

 mum and minimum attractions. The barometrical fluctuations are 

 occasioned by variations in the gravitation of the air towards the 

 earth's centre, — the tidal motions, by the influence of distant hea- 

 venly bodies, — and the magnetic, according to my hypothesis, by the 

 oscillations of the air and aether in their eff"orts to restore the unsettled 

 equilibrium. The three disturbances, therefore, must evidently have 

 nearly the same mutual relations as if they were produced by three 

 forces, one centripetal, and the other two centrifugal, the two latter 

 being nearly equal in amount but diametrically opposed in direction. 

 This leads us at once, theoretically, to the general formula with which 



we started empirically, 



A : B : : B : M, 



and strengthens the conviction that there are none of the pheno- 

 mena of terrestrial magnetism which cannot be explained, either by 

 the instantaneously received and instantaneously transmitted impres- 

 sions which are made directly upon the aether by attraction, heat, or 

 rotation, — by the more sluggish oscillations of the air, which originate 

 from the same sources, — or by the combination of the two. 



Every particle is exposed to the influence of these several impres- 

 sions, the tidal waves of the solid earth having a range, according to 

 Prof. Thomson's calculations (Phil. Trans., Vol. 153, p. 574), at 

 least two-fifths as great as if the globe were entirely fluid. There is, 

 therefore, good reason to hope, that by the application of mechanical 

 laws to the several phases of the fiethereal undulations which produce 

 the phenomena of light, heat, electricity, polarity, aggregation, and 

 diffusion, we may obtain a clearer understanding, not only of all the 

 meteorological changes, but also of seismic tremors, crystallization,''' 

 stratification, chemical action, and general morphology. 



* The phosphorescence that i.s often observed during the process of crystalliza- 

 tion, and the auroral displays in frosty air, are pei-haps owing to analogous vibra- 

 tions. Every chemical, as well as every physical action produces a ponderable 

 disturbance of equilibrium, which must give rise to sethereal oscillations, to 

 which, in their simplest form, we give the name of electric, magnetic, or galvanic 

 currents. 



