120 ASTRONOMY AS A SCIENCE. THE SUN. 



globe, tranquilly diffusing its influences to the planets 

 in surrounding space, but as a vast body, undergoing 

 continual and violent changes on its surface, and, it 

 may be, secular changes also, of which time only 

 can reveal the import and extent, but which, if exist- 

 ing, must assuredly alter some at least of the condi- 

 tions of our own planet. 



But the science of the sun in our own day does not 

 stop here. Known in all ages as the source of light 

 and heat in later times as the centre of planetary gra- 

 vitation, whatever that mysterious force may be it 

 has now become known, though more imperfectly, in 

 its magnetic relations to the earth. This connexion, 

 equally mysterious, is made almost certain by the aver- 

 ages of long observation, involving not only the diur- 

 nal magnetic changes included within the solar hours, 

 but also a seeming periodical coincidence between the 

 maxima and minima of solar spots, and the maxima 

 and minima of magnetic inequalities on the earth. 

 These relations, indeed, require to be attested and 

 defined by further research, comprising as they do the 

 theory of the magnetic force, still imperfect in its very 

 elements, and the physical conditions of the sun's sur- 

 face, not yet fully understood. But their existence is 

 sufficiently proved to carry conjecture beyond, to the 

 probable diffusion in more remote space and among 

 other globes of that elemental force, call it what we 

 will, which we know, as electricity, to be associated 

 with all states, forms, and changes of terrestrial matter, 

 and which we cannot suppose dormant or non-existing 

 among other worlds, subject to the same law of gravita- 



