520 CURTIS— NUMBER OF SPIRAL NEBULA. 



a 6. No. of Small Nebulae. 



1 1" 9™ + 55° 34' 107 



1 1" 22" +17° 46' 69 



12" 15" + 6° i' 81 



12" 55™ + 28° 30' 304 



56? 



his estimate would have been increased by at least 60 per cent, (he 

 found 864 new nebulae in all, and the larger plates he used would 

 have added a number to those counted on the Crossley plates). 



Perhaps all the reasons outlined above may be regarded as con- 

 tributing to an explanation of the difference between Path's estimate 

 of 162,000, and the larger ones due to Perrine and the present in- 

 vestigation. Of these, the possibility noted under {B ), that the small 

 nebulae may conceivably occur in greatest profusion contiguous to 

 the visually discovered obpects of the N. G. C, would appear to be 

 the only reason for changing the larger estimates, and this evidence 

 is only to be secured by taking many additional plates at random. 



In conclusion, I see no reason, at present existing, for changing 

 the estimate made in this paper, that at least 700,000 small spirals 

 are within reach of large reflecting telescopes. Because of the fact 

 that the faintest and smallest members of the class are, in general, 

 discernible only in the more central regions of the plate, I am in- 

 clined to regard the figure given above as, if anything, an under- 

 estimate, and consider it very probable that the total number access- 

 ible may well exceed one million. 



