SIDEREAL ASTRONOMY. 347 



We have spoken of telescopes of large power, because such 

 are essential to nebular astronomy. The great Eerie ctor, for 

 which science is so deeply indebted to Lord Rosse, has by 

 its assiduous direction to the nebulae, afforded three results, 

 each showing the value of the vast telescopic power thus ob- 

 tained. The first of these is the more correct knowledge 

 of the true form and aspects of these wonderful aggregations 

 of stars ; a result well attested by the remarkable differences 

 of certain nebulae as seen through the telescope of six feet 

 aperture, or through one of three feet only. The second dis- 

 covery due to this high power is the extraordinary tendency 

 to a spiral arrangement in these nebular systems ; so fre- 

 quent and so distinctly developed, that it is impossible to 

 attribute it to accident alone. When the volume of the 

 Cosmos now before us was published, only one or two instances 

 of this phenomenon were recognised. They have since been 

 multiplied in the same ratio with the multiplicity and minute- 

 ness of observation; and the results make it needful to 

 suppose a common physical cause for this remarkable effect. 

 The exact and beautiful drawings of these spiral nebulae, 

 which we owe to Lord Rosse's observatory, scarcely leave a 

 doubt that some general law of aggregation and distribu- 

 tion has more or less governed them all. We are compelled 

 however to rest here ; for neither reason nor analogy gives 

 us any knowledge of forces capable of fulfilling these physical 

 conditions. If the attraction of gravitation be still the main 

 element of power, as we have ventured to suppose, it must 



tion Taurus, which he himself had discovered in 1852. A minute star, variable 

 from the tenth to twelfth magnitude, almost touched the nebula, and served to 

 authenticate its position and disappearance. Is this disappearance an obscu- 

 ration from intervening non-luminous matter in motion ? Or is it a change in 

 the luminous or other conditions of the nebula itself? These are examples of 

 the class of questions which such phenomena press upon us. Even unsolved, 

 they bear testimony to the sublimity of the science, which can place these 

 problems before the mind. 



