38 INDEX CATALOGUE. 



Herschel, W. : Abstracts of Memoirs — Continued. 

 A.D. Vol. P. 



1818 108 470 Tig. 1, Plate xxi, represents such a method applied to the 

 foregoing objects. 

 460 IV. Of ambiguous celestial objects. 



An object is often ambiguous when viewed with insuffi- 

 cient optical means, and its nature may be known by in- 

 creasing this means. Objects ambiguoiis to the naked 

 eye become known with the 20-feet telescope, and so on. 



462 V. The milky-way, at the profundity beyond which the gaug- 



ing powers of our instruments cannot reach, is not an 

 ambiguous object. 



463 We may conclude that when our gauges will no longer re- 



solve the milky way into stars it is not because it is am- 

 biguous, but because it is fathomless. 



463 VI. Of the assumed semblance of clusters of stars when 



seen through telescopes that have not light and power 

 sufficient to show their nature and construction. 



464 Observations of various clusters in telescopes of various 



sizes. 



465 Two different principles, the nebulous and the siderial, have 



been observed in the celestial spaces. 

 Distinguishing characteristics of each. 



466 It seems highly probable that some of the cometic, many 



of the planetary, and a considerable number of the stel- 

 lar nebulas, are clusters of stars in disguise. 



VII. Of the extent of the power of our telescopes to reach, 

 into space when they are directed to ambiguous celestial. 

 objects. 



The method of equalizing the light of stars may bo applied 

 so as to give an estimate of the extent of this power. 



"When the united light of a cluster of stars is visible to the 

 [naked] eye, there will be a certain maximum of dis- 

 tance to which the same cluster might be removed, so as 

 still to remain visible in a telescope of a given space- 

 penetrating power ; and if the distance of the cluster 

 can be ascertained by the gauging power of any instru- 

 ment, that will just show the stars of it, the order of the 

 profundity at which this cluster could still be seen as an 

 ambiguous object may be ascertained by the space pene- 

 trating power of the telescope through which it is ob- 

 served. 

 467-8 Examples of this method. 



