1198 
IT. 
Among the older material that may serve for the examination ot 
the variability of Polaris, we must in the first place consider the 
observations executed by G. Mürrer in 1878—81 at Potsdam for 
the determination of the atmospheric extinction and published in 
Vol. III of the Potsdam ’’Publicationen’’. As these observations consist 
in measurements of the differences in brightness between Polaris and 
5 other stars observed in very different zenithdistances, they yield 
abundant material for the determination of the variability of Polaris 
For this purpose I have examined the deviations of these differen- 
ces from their mean value, remaining after correction for mean 
extinction, which are to be found in Müruer’s Table IV, last column 
but one (p. 261—265). Excluded were all observations in which the 
zenithdistance exceeded 60° and all those indicated as uncertain by 
the observer. The others were arranged according to the phase, 
counted from 1879 December 12.0 + nx 37968. The unit of these 
deviations is that of the third decimal place of the logarithm of the 
proportion star: Polaris, i.e. 0.0025 magnitude. In order to give 
the positive sign to the maximum light, the signs must be reversed. 
In the following table are given the normal places formed from 
these deviations reversed in sign and reduced to magnitudes; the 
number of observations on which each normal deviation depends 
has been added in brackets. 
Epoch — Deviation O—C Epoch Deviation O—C 
Dee. 12.02 +0™7022 (25) + 07001 Dec. 14.11 — 0™028 (24) — 07012 
12.34 + 030 (18) 000 14.50 — 009(20) + O15 
12.64 + 047 (23) + O14 14.81 — 009(23) + 013 
12.92 + 008 (20) — 021 15.05 — 021(25)— 004 
13.21 + 028 (18) + 008 15.20 — 048(19)— 036 
13.63 + 006 (20) + 008 15.34 + 017 (24) i 022 
13.84 — 010 Ze — 004 15.69 + 008(29) — 001 
Here also the variability of Polaris appears with unmistakable clear- 
ness and it may be expressed by the following sine-formula: 
Deviation = + 07004 + 07028 sin (p + 35°) 
Maximum Dec. 12.61 = 1879 Dec. 12.57 + 0.14 M. T. Greenwich 
The last column of the table contains the differences Obs.—Cale. 
The mean error of a mean value from about 22 observations is 
07016, hence the mean error of one observation 0™077. 
The immense number of photometric measurements made at the 
Harvard Observatory, in which Polaris has been used as comparison- 
