KNf)\\ Li:i)r,i:. 



NOVKMBF.K, 1912. 



\\ !• liiui licif tlif first j^finis of :i " iuliiil;ir 

 tlicory." Hallt V supposi-d thr lij^lit of tlusc ol)jccts 

 to be occasioned l>y a lucid nudinm diffused through 

 the ether, differing from ordinary matter. .After 

 Haliey, Lacaille and Messier gave more e.xtendcd 

 lists of nebulous objects known to exist in the skv. 

 The last named included one hundred and three in 

 his catalogue of 17.S4. and the letter M. ap|)cnded 

 to a nebula (or cluster) indicates its inclusion 

 in Messier"s list. l^ut the magnificent work 

 of Herschel resulted in tlir disco\-cr\- of a 

 \astl\' greater number : no less than three 

 thousand, mainly discovered by himself, were 

 registered in his catalogues, and he divided them 



.Messier 57 Lyrae (see Figure 4J9) is perha|)S the most 

 interesting. It consists of a nearly circular ring of 

 light with a dark central portion. The latter, 

 however, contains some traces of nebulous matter as 

 seen in the largest instruments, whilst the outer edge 

 of the ring is broken by projections of various 

 sizes and shapes. It has been claimed by some 

 that it is at least jiartly resolvable into stars, whilst 

 the late Sir W. Huggins considered that it is merely 

 a mass of incandescent gaseous or " ultra-gaseous " 

 mattirr, with individual stars scattered over it. Of 

 elliptic nebulae the most remarkable and interesting 

 was for a long time thought to be the great nebula 

 in Andromeda, but as we have said, the photographs 



/Ij' kin.i fcrwissi.K 



Figure 4j0. 

 M. 99 Comae Berenices. 



Figure 437. 

 M. 61 Virginis. 



Spiral Ncbulau photographed at Licl< ( )l5servatory. 



r,.,/,ssor T. J. J. Set. 



Figure 438. 

 M. 88 Comae Berenices. 



into a number of different groups. His work was 

 continued and extended by his son, Sir John 

 Herschel. into the Southern hetnisphere. The two 

 Herschels,, father and son, so thoroughly and com- 

 pletely worked at this subject, that though many 

 nebulae have been added by others to their lists, few- 

 only of these objects are striking, the numerous 

 small faint nebulae now known being visible only by 

 photographic means or the highest telescopic powers. 

 Sir William Herschel made the following classifica- 

 tion, of these objects into six different groups : 



(1) Clusters of stars in which the separate stars are 

 tlistinguishable. (2) Resolvable nebulae, or such as 

 probably would be resolved into stars by increased 

 optical means. (J) Nebulae which show no signs 

 of resolvability. (4) Planetary nebulae. (5) Stellar 

 nebulae and (6) Nebulous stars. To this we must 

 add the sub-divisions of the irnsnl\al)lf or 

 probably irresolvable neliulae. il) Annular nebulae. 



(2) Elliptic nebulae. (.5) Spiral nebulae, the most 

 remarkable and perhajis the most nmnerous of all. 

 (4) Irregular or amorphous nebulae. .\mongst 

 annidar nebulae the well-known ring nebula in Lvra, 



of Dr. Isaac Roberts ha\c brought out its spiral 

 character. Spiral nebulae were for the first time 

 distinctly known to be such when the great tele- 

 scope of Lord Rosse was brought to bear upon 

 these objects. Thus, the Nebula 51M. C'anum 

 V'enaticorum (see '" Kn'OWLT-DGE " volume XX.\I\', 

 page 417). which Sir John Herschel had con- 

 sidered to be a bright globular cluster surrounded 

 by a bright nebulous ring of varying brilliancy, was 

 show n by Lord Rosse to be of a most remarkable 

 spiral form, exhibiting a series of convolutions. 

 -Many other spiral nebulae are now known to exist, 

 and they are to be counted by hundreds, if not by 

 thousands, in the starry heavens. 33M. Piscium 

 and 9<)M. \'irginis are, perhaps, the finest after the 

 nebula in .\ndronieda and the great whirlpool 

 nebula in the " Hunting Dogs." Probably the most 

 beautiful and satisfactory photographs of spiral 

 nebulae e\er taken have been obtained at Lick 

 Observatory. California. L.S. \..by Professor Barnard, 

 the late Dr. Keeler ami Mr. Perrine. with the 

 Crosslev Refractor, and by the courtesy of Dr. See we 

 give reproductions of six of these objects (see Figures 



