190 
case was adopted from Piazzi) — and that of the Bonner 
Sternverzeichniss may be regarded as practically identical 
down to the 9th magnitude.* Assuming with Mr. Pogson 
that the 13th mag. of Argelander’s scale corresponds with 
the 16th mag. of that of Admiral Smyth, we may tabulate 
the mags, below the 9th thus : — 
Mag. Sm. 
Mag. A. 
10 
9*6 
11 
10*1 
12 
10*7 
13 
11*3 
14 
11*9 
15 
12*4 
16 
13*0 
I have not been able fully to verify these results ; but the 
examination of eight stars marked by Sm. as of the 13th 
mag. on three different occasions gave 11*2 mag. as the cor- 
responding mean mag. on Argelander’s scale, presenting a 
satisfactory accordance with the tabulated magnitude. 
The coincidence between the scale of the Bedford Cata- 
logue and that of the Mensurce Micrometricce ceases practi- 
cally with the naked eye magnitudes. At the 6th mag. the 
scales diverge, and the 11th mag. of the one corresponds with 
the 10th mag. of the other. It will be observed that the five 
magnitudes of Admiral Smyth's scale below the 11th are 
represented by only one magnitude in the scale of Professor 
Struve. 
In conclusion 1 may just notice that by a slight oversight 
Mr. Pogson has, in the table to which I have already referred, 
assumed the 12th mag. of Struve’s scale as the limit of vision 
for the Poulkowa refractor of 14*93 inches aperture ; that 
mag. was however assigned by Prof. Struve as the limit for 
# Mr. Pogson has assumed the 8th mag. as the point of divergence of the 
two scales. 
