PHYSICAL SCIENCE. 23 



and assign the place of more than 3,000 other nebulae, re- 

 solving many of them into systems of stars, and by admirable 

 methods obtaining some approximate idea of their distances ; 

 these have been among the undertakings of modern side- 

 real astronomy ; admirably fulfilled by the eminent men who 

 have devoted themselves to this science, the two Herschels, 

 Struve, Bessel, Airy, Argelander, Peters, &c. Sublime even 

 in their simplest enunciation, these problems will be seen 

 to involve results as to space and time which border on 

 infinity; and as such illustrate well those arduous aspira- 

 tions of modern science which it is our present object to 

 indicate. 



Though not easy in a science like this to set limits to its 

 future scope, yet is it difficult to suppose any ulterior dis- 

 covery which can do more than aid in filling up this vast 

 outline. If new laws are discoverable in our own system, 

 we may perhaps presume them to relate to the rotation of the 

 planets on their axes, and to their respective densities ; an 

 important series of facts arbitrary to our present knowledge, 

 but doubtless due to determinate physical causes, and there- 

 fore open to physical research. It is possible, seeing the 

 distances some comets reach in their aphelia, that another 

 planet may exist even beyond Neptune ; which discovery, if 

 ever made, would be so through the observed perturbations 

 of Neptune itself. Certain irregularities in the orbital mo- 

 tions of Mercury have led Leverrier to suspect the existence 

 of an inferior planet, or masses of matter, still closer to the 

 sun; but no actual observation has yet been made which 

 can be admitted as verifying this idea. 



ID the Sidereal system, of which our solar system forms a 

 single part, much yet remains for future completion. Nothing 

 is more wonderful than the phenomena, periodical or other- 

 wise, of the variable stars^ which are now largely catalogued 

 in our books. Ages may be required to gather any certain 



