610 BIBLIOGEAPHY OF HEESCHEL's WRITINGS. 



Herschel, W.: Sykopsis of the Writings of — Continued. 



A. D. Tol. • r. 



suffices. This method may be used to ascertain the profundity of 

 globular and other clusters. 

 1818 108 430 I. Of the distance of globular and other clusters of stnrs. 

 General principles to guide in 8"uch observations. 

 431 II. A series of observations of clusters of stars from xohich the order of 



their profundity in space is determined. 

 431-51 Observations of H. vi, 7, 9, 10, 11, 12, 17, 20, 26, 35, 38, 41, 63, and 

 of M..1, 2, 3, 4, 5, 9, 10, 11, 12, 13, 14, 15, 19, 22, 30, 33, 34, 35, 53, :;5, 

 .56, .57, 62, 67, 68, 69, 71, 72, 74, 75, 77, 79, 80, 92, 97. 

 451 III. Of a method to represent the prof undity of celestial objects in space by 



a diagram. 

 470 Fig. 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 insufiQcient optical 

 means, and its nature may be known by increasing this means. 

 Objects ambiguous to the naked eye become known with the 20-foot 

 telescope, and so on. 



462 V. The milky way, at the profundity beyond which the gauging piotvei's of 



our instruments cannot reach, is not an ambiguous object. 



463 We may conclude that when our gauges will no longer resolve the 



milky way into stars it is not because it is ambiguous, but because 

 it is fathomless. 



463 YI. Of the assumed semblance of clusters of stars whe7i seen through tel- 



escopes 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 sidereal, have been ob- 



served 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 stellar nebulse, are 

 clusters of stars in disgiiise. 

 466 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 be 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 distance 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 in- 

 strument, that will just show the stars of it, the order of the pro- 

 fundity at which this cluster could still be seen as an ambiguous 

 object may be ascertained by the space-penetrating power of the 

 telescope through which it is observed. 

 467-70 Examples of this method. 

 470 Plate XXI. 



William Hersch'kl. 

 [Dated] Slough, near Windsor. 



