132 ANNUAL REPORT SMITHSONIAN INSTITUTION, 19 42 



scopes. Under such conditions, it is always possible that the re- 

 sults may be affected by hidden systematic errors. Although no 

 suggestion of such errors has been found, the possibility will persist 

 until the investigations can be repeated with improved techniques and 

 more powerful telescopes. Ultimately, the problem should be settled 

 beyond question by the 200-inch reflector destined for Palomar. The 

 range of that telescope, and the corresponding ranges of the dimming 

 corrections, should be about twice those examined in the present in- 

 vestigations. Factors of 25 percent in the apparent brightness of 

 nebulae at the limits of the spectrograph, and 40 to 50 percent at the 

 limits of direct photography should be unmistakable if they really 

 exist. 



Meanwhile, on the basis of the evidence now available, apparent 

 discrepancies between theory and observation must be recognized. 

 A choice is presented, as once before in the days of Copernicus, be- 

 tween a strangely small, finite universe and a sensibly infinite uni- 

 verse plus a new principle of nature. 



REFERENCES 



No extensive bibliography is furnished because the list would be largely :i 

 repetition of the carefully selected bibliography compiled by H. P. Robertson 

 as an appendix to his discussion of "The Expanding Universe," published in 

 Science in Progress, Second Series, 1940. Robertson's contribution to the series 

 is the clearest nontechnical presentation of the fundamental problem of cos- 

 mology that has yet appeared. 



A few papers, subsequent to Robertson's bibliography, are listed below. 

 EuDiNGTON, Sir Aetiiur. 



1940. The speed of recession of the extragalactic nebulae. Festschr. fiir 

 Elis Stromgren, Copenhagen. Derives the rate of expansion as 

 an apriori datum, and finds a numerical value agreeing Avith the 

 observed value within the uncertainties of the data. 

 HxjBBLK, Edwin. 



1939. The motion of the galactic system among the nebulae. Journ. 

 Franklin Inst., vol. 228, p. 131. Cites evidence suggesting that the 

 law of red shifts does not operate within the local group. 

 Shapley, Harlow. 



1938-1941. Various discussions of counts of nebulae, and their bearing on 

 the problem of the general distribution. Proc. Nat. Acad. 

 Sci., vols. 23-26. Emphasis is placed on small-scale irregu- 

 larities of distribution and the role played by the great cloud 

 of nebulae in Centaurus. 



