18 



Herman Schultz, 



Before summarily indicating the contents of the columns in the tables 

 of the observations in general, it will yet be necessary somewhat at large 

 to give a relation of the double-col. 7, which contains descriptions of the 

 nebulae by means of numbers nearly according to a project made for that 

 purpose by Sir John Herschel, but which has never since come into prac- 

 tical use. This mode of description, which is very commodious and to the 

 use of which it is very easy to accustom oneself, offers moreover many 

 advantages, so that in my opinion it is well worth the general acceptance 

 of nebula-observers. The description is in the first place quite independent 

 ot the language of the observer, which is here no small advantage; the 

 description is further obtained without the troublesome use of many and 

 often doubtful terms and in a so concise form, that it in an instant can 

 be looked through, which for example in the comparison of the nebulae with 

 each other is of the greatest consequence; while on the other hand the de- 

 scriptions are so precise and complete as in the most cases can possibly 

 be desired, whenever the matter before us is not a monographical study 

 of a single object. 



For the nebula-observers it is a well known fact, that in his Results 

 of Astronomical Observations made at the Cape of Good Hope (pp. 137 — 143) 

 Sir J. Herschel has discussed the question of classification of nebulae and 

 that at pp. 140 — 143 is proposed the project here adopted by me. He di- 

 vides the nebulae in their widest sense into 3 classes: 



Class I containing regular nebulae. 



Class II — irregular nebula}. 



Class III — irregular clusters. 



To Class I are reckoned all nebulae, that have a more or less evidently 

 prominent centre of condensation, or in which the nebulosity with some 

 degree of regularity is symmetrically lodged around a certain determinate 

 point. Sir J. Herschel himself describes these objects in the following termes 

 (1. c, p. 140): 



"The normal form of what may be called Regular Nebulce is the El- 

 liptic, admitting every degree of ellipticity, from the spherical to the linear 

 form; every law of condensation, from the circumference to the centre of 

 the apparent outline, from a uniform disc to a starlike centre, surrounded 

 with faint and gradually fading nebulosity; every grade of brightness, from 

 an object like o Centauri distinctly visible to the naked eye, to the feeblest 

 third-class nebula, barely discernible with the best telescopes; and every 

 shade of resolvability, from stars distinctly numerable even in the middle, 



