Introduction 
iii 
measures or description of Herschel I. Many of these have been identified for this work, and are 
given with corrected places. A few of the others, from lack or vagueness of description, can not 
be identified with any certainty. 
The measures of Sir John Herschel as a rule are confined to a single setting for the posi- 
tion-angle, and an estimate of the distance. Generally these angles are in fair agreement with 
later measures when these stars have been re-observed. Change could only come from proper 
motion in pairs of this class. Later measures will show whether or not some of the apparent 
changes are real. Most of the Herschel estimates of distances are too large, and particularly of 
stars under 10 '. 
Column 8. Magnitudes. The magnitudes of the components are given from the same source 
from which the measures are taken. The scale employed by Struve, Otto Struve, Dembowski, and 
all the later observers is practically the same. That of Herschel II gives much higher numerical 
values for the magnitudes of telescopic stars. He gives the following corresponding values derived 
from a large number of comparisons of his estimates with those of Struve : 
H 2 
H 2 
H 2 
6.0 = 5.5 
10.0 = 8.8 
14.0 = 10.5 
6-5 = 5-9 
10.5 = 9.1 
14.5 = 10.7 
7.0 = 6.4 
11.0= 9.3 
15.0 = 10.9 
7-5 = 6.8 
11.5 9.6 
16.0 = ii. i 
8.0 = 7.3 
12.0 = 9.8 
17.0 = 11.4 
8.5 = 7.7 
12.5 = 10.0 
18.0 = 1 1.6 
9.0 = 8.1 
13.0 = 10.2 
19.0 = 1 1.8 
9-5 = 8.5 
13-5 = 10.4 
20.0 = I2.O 
It is a fact worth noting that there is no satisfactory evidence of variability in the relative 
magnitudes of the components of any real double star, although distant stars have been occasionally 
connected with other stars in which there is some change. 
Column 9. Date of measures cited in columns 6 and 7. 
Column 10. The astronomer whose observations are given, and the number of nights on which 
complete measures were made. In many instances the angle was measured on other nights, which 
enter into the mean result given, but it cannot be presumed that they add much, if anything, to the 
value of the mean when the difficulty of the object, from the closeness or inequality of the com- 
ponents, made it impossible or undesirable to attempt measures of distance. The number of nights 
attached to the measures cited in Part II is that on which complete measures of angle and distance 
were made. 
Column ii. Brief notes relating to the several components connected with the principal star; 
the colors given by Struve for his stars, by Dembowski for the Otto Struve stars ; and references to 
the original authority from which the pair is taken when there are no subsequent measures and the 
citation is brief enough to be given in this column. There is too much uncertainty in most of the 
observations of color, particularly of the smaller stars, and of the larger stars where the color is not 
of a decided character, to make it worth while giving any comparison of the various results which 
would necessarily present large differences. 
APPENDIX TO PART I 
While this work was going through the press, a great many new double stars were found by 
Aitken and Hussey at the Lick Observatory, which were received too late for insertion in their 
proper places in Part I. For the sake of completeness, and by way of bringing the catalogue of known 
pairs down to the latest date possible (1906), it seemed desirable to add these discoveries in the 
form of an appendix to Part I, and this has accordingly been done. The star places are for 1900, 
as given in the several Lick Observatory Bulletins from which they are taken. 
