Observations of 500 Nebulae. 



21 



to be brighter than a star of the 9 Hl magn. (Besselian scale), those of the 

 5 th class to be fainter than a star of 12,5 magn., and the middle-bright 

 (cl. 3) to correspond in brightness to stars from about the 10,5 to about the 

 11,5 magn. But, as those estimations in many cases must become extre- 

 mely difficult, it is evident, that here nothing like a higher degree of pre- 

 cision can be expected. 



Roundness (col. 3). 



3 length not more than double the breadth. 



4 length not exceeding 5 times the breadth. 



5 length 5 times the breadth or more. 



Condensation (col. 4). 



In this col. of our scheme a * is inserted in the 6 th line to remind the 

 reader of the following notation: 



if the nebulai of the degrees of condensation 2, 3, 4 have a star in the 

 middle, and which in such cases is of course the point observed, I put 

 in the 4 th place of their description respectively * 2, *3, *4; and, it 

 nothing is said of the condensation, simply a *. 



Resolubility (col. 5). 



2 resolved part of the nebula quite or nearly free from nebulosity. 



3 single stars steadily visible on nebulous ground, or only momen- 

 tarily seen glimmering through the nebulosity. 



Lastly it is to be remarked, that a zero in any of the descriptive co- 

 lumns always indicates . that no description in that respect could be obtained. 

 After the 5 places of description the magnitude of the nucleus or of the 

 central-star ( * ) is indicated according to the Bessel-Argelandrian scale. When 

 the object observed is a star, its magnitude merely is given in the descrip- 

 tive column 



This may be best illustrated by a few examples: 

 321. 1. 3 (10) = nebula, on an average 1' to 2' in diameter, of the brighter 

 ones of W. Herschel's class I; nearly circular; with a nu- 

 cleus of the 10 th magn.; nebulosity with more or less evident 

 traces of resolubility. 



