KUNGL. SV. VET. AKADEMIENS HANDLINGAR. BAND 60. N:0 8. 15 



Joy's data give ra =13,o; ra = 12,i3, from which follows: 



1C Ml „ = 0",0005ö0 



and 



s' = 0,017. 



The leaving out of the two values for s r , that were obtained from Mil and M 37, 

 does not alter anything as to the final result. For if we considered all 4 clusters, 

 we should obtain: 



M3 



s' = 0,010 



M 13 



009 



Mil 



27 



M37 



17 



0,01G, 



a value of the same order as the one determined from M 3 and M 13. 



Another reason in excluding Mil and M 37 is to be found in the circumstance 

 that no data exist on the frequency of the B — B b stars, and that, accordingly, the 

 parallax cannot in this case be derived from the luminosity-law with the same cer- 

 tainty as has been possible for the two other clusters. 



Under the supposition that the luminosity-law has the same form in clusters 

 as in the stellar system, we can, starting from the form for B (ra) given by photo- 

 metric measurements, deduce by the graphic method parallaxes for clusters by 

 removing the curve for B(m), until it coincides with f(M), which, as we have suppo- 

 sed, has for all spectral classes the form corrected and established by van Schouten, 

 and for the classes B — B b , B h — Z? 9 , A — A 9 the form, deduced from the corre- 

 sponding frequency-curve3 given in (7) — (9). 



We obtain by this method: 



"i/a "A/13 



0",000022 0", 000045 1 _ „ 



}fcrom all colours 



32 22 j 



40 130 From the colour-classes b —b b 



96 240 » » ~ » &i — & 9 



174 » > » a — a s 



0",000075 0",000109 



which gives: 



s =0,0053. 



If we employ van Schouten's method, which also implies a comparison between 

 the form of the luminosity-curves — with the difference that he does not compare 

 the curves entire, but section by section — we obtain: 



