610 BIBLIOGRAPHY OF HERSCHEL's WRITINGS. 



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

 A. D. Vol. r. 



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

 glohiilar and other clusters. 

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

 General principles to guide in such ohservations. 

 431 II. J scries of observations of clusters of stars from which the order of 



their profundity in space is determined. 

 431-51 Observations of H. \i, 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, CS, 

 .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 hy 



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 insufficient optical 

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

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

 telescope, and so on. 



462 V. The milky tvay, at the profundity beyond ichich the gauging potcers of 



our instruments cannot reach, is not an ambiguous object. 



463 We may conclude that when our gaviges 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 when seen through tel- 



escopes that have not light and power sufficient to shoiv 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 nebula?, are 

 clusters of stars in disguise. 

 466 VII. Of the extent of the po^ver of our telescopes to reach into sjmce 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 Herscht-l. 

 [Dated] Slough, near Windsor. 



