Chase. J 104: [April. 



are also earth-currents, which exert an appreciable raodifying influ- 

 ence. I am confident that they will be found equally obedient to 

 the laws of gravitation, which affect every particle of the earth's 

 body, modifying the crystalline polarity and cohesion of solids as well 

 as the flow of liquids, and producing internal tides, which may con- 

 tribute largely to that metamorphism of stratified rocks which has 

 been referred by geologists to the agency of heated fluids and vapors. 

 (See Rogers, Pa. Report, 2,700 ; Lyell, Amer. Jour, of Science, [2], 

 39,22.) 



The inclination presents some anomalies that are difficult to ex- 

 plain, and whether we compare the solar-diurnal or the annual curves 

 at the principal northern and southern stations, the " indications of 

 a difference in the morfc of operntion of the solar influence in the 

 two cases" seem as striking and perplexing, as they did to Hudson 

 and Herschel in their examination of the influence of heat on the 

 barometer (Proc. A. P. S. IX, 283), and to Sabine, in his discus- 

 sion of the semi-annual declination curves (St. Hel. Obs., 2, cxix). 

 But the disappearance, in the progress of our investigations, of these 

 once seemingly insurmountable difficulties, — the wonderful coinci- 

 dence in the general features of the gravitation and magnetic cur- 

 rents, — and the a priori probability that all disturbed forces, of 

 whatever character or variety, will tend constantly to a mutual 

 equilibrium, — encourage the belief that this apparent paradox may 

 be likewise susceptible of a simple interpretation which will drive it 

 from its latest lurking-place. 



I can think, at this moment, of no more probable causes of the 

 want of symmetry here spoken of, than the different distribution of 

 land and water in the two hemispheres, and the influence of power- 

 ful alternating land and sea breezes.* A long series of connected 

 observations at a number of new stations may, perhaps, be required, 

 before it can be satisfactorily ascertained whether the disturbances 

 thus occasioned are sufficient to account for all the phenomena, but 

 meanwhile it is interesting to observe the degree of accordance that 

 exists at northern inland stations, like Philadelphia and Toronto, 

 between the curves of vertical force and force of wind on the one 

 hand, and those of horizontal force and barometric pressure on the 

 other, as well as the agreement that has been pointed out by Dr. 

 Lloyd and Mr. Homer, between the annual curves of declination and 

 of temperature. 



* The dependence of declination upon land lines and ocean currents, 

 is shown by isogonic charts. 



