J83H 



• 



Aiiutlier means ol' [)eiielrati!ig still furtlier are the plates taken 

 by Fkanklin-Aüams; according to Chapman and Melotte they go 

 below the 17''' magnitude (photogr.), which is also proved by the nnra- 

 l)ers tiiey give. For the galactic zone the nnmber N for the magnitnde 

 15,0 16,0 17,0 according to their original statements was 650,1300, 

 2050; these numbers, on account of erroneous formation of mean 

 values are too small, and later on Dr. ChaPiMan gave for the two 

 former 840 and 1700 (%.V2,92 and 3,23)^) that is 29V„ and 317» 

 more: if therefore we take the latter 33 ", „ larger, tiie number foi" 

 17,0 becomes A' =r 2800. The table of van' Rhun for these A' gives 

 the photographic limiting magnitudes 15,2 16,2 ami 16,9, which 

 proves that the stars up to 17,0 have been incompletely counted. 

 From the values of N, deducted in Gron. Publ. 18 for Hekschei, 

 viz. A' = 175,6 373 1023 for the 3 zones 40— 90, 20— 40 and 

 0—20 galactic latitude, follows the photographic limiting magnitude 

 for HkkschI'',!, 15,30 15,18 and 15,17. The countings therefore, indi- 

 cated by Chapman and iMelottk with 17,0, penetrate U magnitude 

 further into the faint stars than Hehschkl's gauges. 



The separate countings on plate 136 (A.R. 20^',0 : decl. 15°) con- 

 taining the region of Acpiila. have been kindly put at my disposal 

 by Prof. Dyson. FoV this plate the limiting magnitudes have not 



dlog A 



been determined pholometricallv, so tiiat cannot be strictly 



dm 



deduced. If for the ;// the average \ allies are taken, then we tind 



(as the a\ei'age of 6 regions, situated in the Galaxy in Aquila and 



Sagitta) 



m=il4,4 15,3 16,:i 17,0 



A' =905 3445 11883 14310 



(/ log N 



—^ — = 0,61 I», 53 0,12 

 dm 



This last difference once more proves that Chapman and Mklottk 

 have counted the faintest stars very incompletely, in these dense 

 galactic regions even more so than elsewhere. Also in the other 

 dilferences little is to l)e detected of the strong gradient that might 

 ha\e been expected from Hkkschkl's numbers. Chapman has treated 

 also the densest parts of the galactic zone separately, and finds 

 for it : 



for m— 18 14 15 16 



loQ N = 2,68 3,07 3,37 8,60 



') S. Chapman. The number and galactic distribution of the stars. Table A 

 Monthly Notices 78. p. 70. 



