( 118 ) 



"The lal (er (the stars) are vastly more numerous in the regions near 

 the Milkj' Way, and fewer in number near the poles of that belt. 

 But the reverse is the case with the nebulae proper. They are least 

 numerous in the Milky Way and increase in number as we go from 

 it in either direction." 



Cleveland Abbe who after the publication of Joux Hkrschel's 

 catalogue in 1864 statistically iuvesligaled this peculiarity (Month. Not. 

 R. A. S. XXVII, p. 257) rightly put the question whether the paucity 

 of nebulae in the Galaxy did not rest upon a mere optical delusion 

 due to the luminous l)ackgroiiud of the Milky Way. He thought 

 himself justified, however, in answering this question in the negative, 

 because the regions on eithci- side of the Galaxy proper did not show 

 a considerable increase in the number of nebulae; nor was liiis tlie 

 case with increasing optical power. 



With a much more extensive material — 92G4 objects — »Str.vtonoff 

 (Publ. Tachkent N". 2) arrived at cliietly the same result. With some 

 reservation, however. For in fact if we develop Stratoxoff's data in 

 a somewhat different way we find that, as we go from the galactic 

 plane, the faint nebulae increase more rapidly than the bright ones. This 

 fact, also because it contradicts a preliminary result of Max Wolf : 

 tliat the (photographed) small nebulae are in general distributed more 

 ecpuilly over the sky, raises the surmise that in visual observation 

 the light of the smallest and faintest nebulae in the gah\c(ic region 

 is to a certain amoujil extiiiguished (table I). 



TABLE I. 



Increase of the mean density of bright and faint nehulae in the 

 direction from the Galaxy. 



,, 1 1 .-x 1 Bright nebulae Faint nebulae 



Mean gal. latitude ^ ° .,, ^ .xt ^ •. , . 



" (N. brillantes) (N. faibles) 



+ 35° 7.5 10.2 



+ 25° 3.8 7.0 



-\- 15° 2.3 3.4 



+ 5° 1.9 1.5 



— 5° 2.3 1.8 



— 15° 3.7 5.1 



— 25° 6.2 IJ.O 



— 35° 6.5 12.5 



In order to investigate this problem more fully I have compared 

 tl^e density of nebulae in the different parts of the northern Galaxy 



