476 Letter from B. A. Gould. 
indisposed to believe that stars ea below 64 or 6°6 could be 
visible to the naked eye. Experiments made with cabs reba 
failed to give a eaGuteclore restilt, a shits I fixed upon 65 as 
aided eye being considered as below 6°7. The work had far 
aavinged before the arrival of any means of accurately testing the 
oo of this assumption; and my suprise was great when 
er mparison of the faint stars within the espera with 
‘Argelander’s “Durchmusterung” and Bessel’s zones, there re- 
mained no room re doubt that the — which we had been 
calling 6°5 was in reality not more than 7°0; and that on the 
clearest nights ohare not brighter than 7-2 could be distinctly seen, 
ea considerable number which had been seen and recorded 
are not above the 7°5 magnitude. This is beyond all question, 
and ee at once the transparency of our sky, and the sharp 
of our observ 
that the limit ought not to be brighter than 7 t was no 
difficult to translate cet agnitudes recorded into the correspond- 
ing true ones, since t of the stars had been observed two OF 
seem. 
the limits of vision ; Shite any systematic ed to diversity ri 
the estimates of the several observers. cou uld be at once recognize 
Th 
and their places reduced to the adopted “tas For this rig 
ion a large number of additional faint stars have been added t 
the catalogue in the belt—those only being adopted as stant 
ards of magnitude to which all four observers assigned the sam 
Swing The scale thus established has been similarly ei ag 
