Li. C. Pickering—Light of Comparison Stars for Vesta. 17 
barometer at Denver had already descended °43 inch. A sim- 
ilar case occurred between April 8 and April 10, 1874. This 
cause of the discrepancies between the observed and computed 
reductions, seems to be more efficient for Pike’s Peak than for 
Mt. Washington. The third cause above mentioned affects the 
observations on Pike’s Peak, but in general the curve of pres- 
sure for Pike’s Peak is much less jagged than for Denver. 
The barometer on Pike’s Peak frequently remains above its 
mean height for several days—sometimes a week or ten days— 
with only small fluctuations, while during the same period at 
Denver there have been numerous maxima and minima of con- 
siderable magnitude. Thus it sometimes happens that a baro- 
metri¢ maximum on Pike’s Peak occurs nearly, if not exactly, 
at the time of a barometric minimum at Denver. : 
[To be continued. ] 
Art. Il.—Light of Comparison Stars for Vesta; by EDWARD 
; C. PICKERING. 
In Professor Harrington’s important “Study of Vesta,” which 
appeared in this Journal, III, xxvi, 461, the light of the 
planet was determined from comparisons with the two stars 
DM. +22° 2163 and 2164. The observations were made with 
the wedge photometer, and were accordingly differential, so that 
the resulting magnitudes of Vesta depend upon the assumed 
magnitudes of the stars, which were taken from the Durchmust- 
erung. It therefore appeared desirable that the stars should 
be observed with the large meridian photometer of the Harvard 
College Observatory, with the object of providing means for the 
reduction of Professor Harrington’s results to absolute measures. 
The meridian photometer has been described in the Monthly 
Notices of the R. Astron. Society, xlii, 365. 
The following table exhibits the results respectively obtained 
for the two comparison stars. The first column contains the 
numbers of the series to which the observations belong, the 
second the dates, and the third the initials of the observers, E. | 
C. Pickering and O. C. Wendell. The fourth and fifth columns 
contain residuals expressed in tenths of a magnitude. The 
mean results, from which these residuals are derived, when cor- 
rected for atmospheric absorption, are 9°06 for DM.+22° 2168 
and 5:48 for DM.+22° 2164. The fifth observation of DM.+ 
22° 2163 was rejected because it appeared that an error of 30° — 
In reading the graduated circle of the photometer had probably 
occurred in one of the four comparisons which constitute a 
complete observation with the meridian photometer. The resi- 
dual corresponding to the rejected observation is placed in brack- — 
Am, Jour, Sct.—Turep Serres, Vou. XXVIII, No. 163.—Juny, 1884, Sas 
2 Sil os , 
