AMERICAN 



JOURNAL OF SCIENCE AND ARTS. 



[THIRD SERIES.] 



Akt. XLll— On supposed changes in the Nebula M. 17 = b. 

 2008 = a C. 4403. (R. A. IS^ 12"' 33«.l ; N. P. D. 106" 

 13' 36" ; 1860-0) ; by Edward S. Holden.* 



I. Historical Notes — Observations: — This nebula was discov- 

 ered bv Messier and is number 17 of his list {Connaissance des 

 Terns 1784). It has been carefully studied since 1800, by Sir 

 John Herschel (1833-37), Lamont (1837), Mason (1839), Lassell 

 (1862), Huggins (1865), Trouvelot (1875), and Trouvelot and 

 myself (1875). These observations, so far as they are pub- 

 lished, are to be found in the following works :— 

 Heeschel: Observations of Nebute, etc, made at Slough; PMl. Trans., 1833, p. 



498 and Plate XII, fig. 35. 

 Heeschel : Results of Astronomical Observations at tJie Gape of Good Hope, p. 8 



and Plate IL fig. 1. 

 Lamont : [/eber die ^ebeljieckm, 1831, fig. X. 

 Lamont: Annalen der K. Sternwarte hei MUnchm, band xvii, p. 332 and fig. 21, 



Plate VIII. 

 Mason: Transactions American Phil. Soc, vol. vii, 1840, p. 165, Plate YI. 

 Lassell: Mmi. E. A. S.. vol. xixvi; Plates VII, VIII. figs. 33, 33 A. 

 HiTGGiNS: Pkilosopical Transactions 1866, p. 386. 



The later observations are unpublished. 



I extract from these various authorities such portions as will 

 be of use for subsequent reference. 



From Herschel's paper {Phil. Trans., 1833):— 



" The figure of this nebula is nearly that of a Greek capital 

 ojnega, n, somewhat distorted, and very unequally bright. 

 Messier perceived only the bright [eastern] branch of the nebula 

 now in question, without any of the attached oon\;olutions which 

 were first noticed by my father. The chief peculiarities which I 

 * This article has in 



Messrs. Appleton 

 t- JoDR. 8ci.— Third Sbries, Vol. 



