142 



NATURE 



[December i, 1910 



in process of formation. In general they lie in streams 

 which follow the curvature of the convolutions. Together 

 with the smooth nebulous material in which they are 

 apparently floating, and out of which they are apparently 

 forming, they constitute the convolutions." 



While a detailed study of individual nebulae endorses 

 the meieoritic hypothesis regarding the formation of 

 stars, the hypothesis itself requires the presence of a 

 considerable quantity of self-luminous or non-luminous 

 matter scattered throughout space. The recent ad- 

 vances in the photography of nebulae have, however, 

 very considerably altered the. g^enerally conceived 

 notions regarding the amount'6f nebulous matter dis- 

 tributed in the heavens. After Keeler turned his 

 attention towards photographing nebulae, he soon 

 found that he was able considerably to increase the 

 number of known nebulae with the aid of the Crosslej 

 reflector. In this research he reached 

 two important conclusions : — 



(i) " Many thousands of unrecorded 

 nebulae exist in the sky. A conservative 

 estimate places the number within reach of 

 the Crossley reflector at about 120,000. 

 The number of nebulae in our catalogues is 

 but a small fraction of this!" (2) " Most 

 of these nebulae have a spiral structure." 



In the preface to the volume contain- 

 ing Keeler 's photographs it is stated :— 



" The number already discovered and 

 catalogued did not exceed 13,000. Later 

 observations with the Crossley reflector, with 

 longer exposure-times and more sensitive 

 plates, render it probable that the number 

 of nebulae discoverable with this powerful 

 instrument is of the order of half a 

 million." 



While the above estimate relates to the 

 capacity of the Crossley reflector, what 

 number of additional nebulae should be 

 added when the very much greater 

 efTficiency and aperture of the Mount 

 Wilson Observatory's reflector is taken 

 into account? Prof. Ritchey, as has 

 been shown above, has demonstrated the 

 far-reaching capacity of this instrument 

 and its enormously improved efficiency 

 for ne'Bular photography. Further, when 

 the loo-inch reflector of the same 

 observatory is brought into use, what 

 will then be the approximate number of 

 known nebulae? 



Again, while all these instruments can 

 onlv record the existence of self- 

 luniinous matter in space, what estimate 

 should be made for the number of re- 

 gions in the sky in which matter which 

 is not luminous is present? The only 

 conclusion that can at present be drawn 

 IS that amount of matter distributed in 

 space is really enormous compared to 

 that which is generally conceded to be 

 the case. If, as very probably is the 

 case, this non-luminous matter is as fre- 

 quently distributed as that w-hich is 

 luminous, then any hypothesis to explain 

 inorganic evolution must be founded on 

 a meteoritic basis. 



The work of modern large reflecting telescopes in 

 adding to our knowledge of the probable amount of 

 nebulous matter in space is of verv great importance, 

 and the magnificent success of Prof. Ritchey in his 

 latest achievement forms another opportunity for the 

 hearty congratulations of all astronomers to be ex- 



NO. 2144, VOL. 85] 



tended to him. Prof. Ritchey is to be envied, not only 

 for working in a country where astronomy in all its 

 branches is so well fostered, but for being one of tiie 

 members of the staff of the Solar Observatory on 

 Mount Wilson, an observatory which is so magnifi- 

 cently endowed. On that mountain, when it is. 

 decided that a spectroheliograph, which we in this 

 country would consider of very large dimensions^ 

 would be capable of accomplishing better research, 

 if another of double its size were instituted, then 

 promptly the necessary funds are forthcoming, and 

 the instrument is taken in hand, built, and brought 

 into use. Again, no sooner is a 60-inch mirror found' 

 to be a very great advance in celestial photograph}' 

 than one of 100 inches in diameter is immediately pro- 

 jected, and all necessary arrangements for its com- 

 pletion and erection are made. With such facilities 



Y\G. 3. — Spiral Nebula Messier 51 Canum Venaticorum. Photographed with the 60-inch 

 reflertor and the new plate carrier. Exposure 3h. 55m., February 7 and 8, 1910. Notice 

 the roundness of the star images. 



for research, so incentive to those who are employed 

 in the investigations, no wonder that work of the 

 highest quality and importance can be turned out; 

 for this reason this country, like many others, is being 

 left far behind. 



William J. S. Lockver. 



