142 CELESTIAL PHENOMENA. 



remote; while the other, composed of stars alone, is 

 less distant. The latter ring, or that to which we 

 usually apply the term "Milky Way," consists of stars 

 averaging from the 10th to the llth degree, but ap- 

 pearing, when viewed singly, very various in point of 

 magnitude; whereas detached clusters, or groups of stars, 

 almost always shew throughout great similarity in mag- 

 nitude and brilliancy ( m ). 



In whatever quarter the celestial vault has been exa- 

 mined with powerful space-penetrating telescopes, either 

 stars, though it may be only telescopic ones from the 

 twentieth to the twenty-fourth degree of magnitude, or 

 nebulae, are seen. It is probable that, with still more 

 powerful optical instruments, many of the nebulse would be 

 found resolvable into stars. The sensation of light, impressed 

 on the retina by single isolated points, is less, as Arago has 

 recently shewn, than when the rays proceed from several 

 points extremely near to each other ( 116 ). It is probable that 

 the production of heat by the condensation of the cosmical 

 nebulous matter, whether existing in definite forms, or 

 simply in its general state of distribution, may modify the 

 equable intensity of light, which, according to Hallcy and 

 Olbers, should arise from every point in the heavens being 

 occupied by an infinite series of stars ( 116 ). Observation, 

 however, contradicts the hypothesis of uniform distribution, 

 shewing us instead, extensive regions wholly devoid of stars 

 ' openings in the heavens," as William Herschel calls 

 them one four degrees in width in Scorpio, and another in 

 Ophiucus. We find near the margin of both these open- 

 ings resolvable nebulse, of which the one on the western 

 edge of the opening in Scorpio is amongst the richest and 



