NEBULA, CLUSTERS, ETC. 21 



Hersctel, W. : Abstracts of Memoirs — Continued. 



A.D. Vol. p. 



1785 75 258 Enumeration of very compound nebula or milky way. 



Ten described, including that of Orion and Andromeda. 

 263 Account of nebula of Lyra. G. C, 4447. 



Planetary nebulae. Observations of G. C, 4628, 4964, 



4572, 4565, 826, 2102, 4302. 

 The accompanying plate gives a figure of a section of the 



milky way. 



1786 76 457 Catalogue of one thousand New Nebulce and Clusters oj 



Stars. 

 Description of sweeping telescope ; Newtonian ; 20 feet 

 focus, 18.7 in. aperture, power 157, field 15 / 4". 

 458 Description of the method of sweeping. 

 464 Probable errors of the places given by the sweeps before 

 1783, Dec. 13, Aa = l m , Ad S'-IO', during 1784 Aa 

 < 30 s , AS <5'. 



Till 1785, September 24, Aa < 12 s , Ad <4'. 

 After 1786, April, Aa < 6 s , A6 < 2'. 



466 Definition of classes of nebulae and clusters. 



467 A map of positions of nebulae was made for identification. 

 469 Explanation of a short method of describing appearance of 



nebulae by letters. 

 471 Catalogue : 



Class I No. 1 to No. 93 



II No. 1 to No. 402 



III No. 1 to No. 376 



IV No. 1 to No. 29 

 V No. 1 to No. 24 



VI No. 1 to No. 19 

 VII No. 1 to No. 17 

 VIII No. 1 to No. 40 

 498 Notes to special nebulae. 

 1789 79 212 Catalogue of a second thousand of New Nebula and Clusters 

 of Stars ; with a few introductory Remarks on the Con- 

 struction of the Heavens. 



213 A telescope has power to penetrate into space. Proof that 



every star is a sun shining by its native brightness. 



214 Systems of stars— globular clusters and definition of a clus- 



ter. 



216 Admitting that a cluster is real, not apparent, the stars com- 



posing it are about of equal magnitude. 



217 At the same distance from the centre an equal scattering 



takes place. 

 These clusters are of a globular form. 



218 They are more condensed at the centre than at the surface. 



