Introduction 
at the top of each page, so that any star can be found when its general number or right ascension 
is known without first consulting the tabular part. 
As far as practicable the proper motions of the principal stars have been taken from the best 
sources of information, and to make them immediately available for double-star purposes, the values 
from meridian observations in right ascension and declination have been reduced to arc, and given 
with the direction of the motion in position-angle. Many of these proper motions are small, and 
probably somewhat uncertain in amount and direction, but in some instances they are confirmed 
generally by the measures of the companion, or of some star in the field. When these measures are 
separated by a considerable interval of time, as they are in many of the old pairs, the proper motion 
thus found should be very exact. Most of the comparison stars are relatively faint, and may be 
considered as practically fixed in space. The instances where the small star has any sensible 
proper motion of its own are comparatively rare, so far as appears from micrometrical measures, 
and when a different value is found for the primary from observations connecting it with some 
small star, it would be unsafe in the great majority of cases to infer that therefore the comparison 
star was moving in space. Examples of stars of very different brightness drifting at practically 
the same velocity are not uncommon, and presumably they have some physical relation to each 
other, even when they are separated by distances considerably exceeding that of any of the known 
binaries. 
It was my purpose to present in Part II late measures of every important star of the older 
catalogues, including all of the pairs in the Dorpat and Pulkowa catalogues, as well as all the stars 
of the several classes in Herschel I which were too wide to be included in the Mensurae Micro- 
metricae, and like pairs in the lists of South, and Herschel and South, and also the most prominent 
stars in the seven catalogues of Herschel II which from the magnitude of the primary and the 
estimated distance between the components would presumably make them worthy of re-observation. 
In the interest of this work I have given something more than five years' time with the 40-inch at 
the Yerkes Observatory; and nothing in the way of other micrometrical work, however important it 
might appear to be in the line of other investigations, has been allowed to interfere with carrying out 
this programme. 
As would be expected, the time which could be given to this work of 104 nights per year, 
making altogether only about 1,200 observing hours, assuming every night to be clear throughout, 
proved to be insufficient to complete the observations of so extensive a working-list, although some 
eight or ten thousand measures were made of these stars. 
This part of this work is greatly indebted to Professors R. G. Aitken and Eric Doolittle for a 
large number of very recent and unpublished measures of classes of stars where late measures are 
specially important. The measures at the Lick Observatory are generally of very close and difficult 
pairs, many of them in rapid motion, and nearly all of the class which can be better measured at that 
place than anywhere else. The observations at the Flower Observatory are largely of the pairs 
discovered by Professor Hough at the Dearborn Observatory, many of which have not been 
measured since the first position was published. Professor Hussey, while at the Lick Observatory 
(1898 to 1904), made a large number of measures of the Struve stars which are still unpublished, 
and these are given in the notes; and also a few measures made at the Kirkwood Observatory, 
principally by Professors John A. Miller and W. A. Cogshall. 
APPENDIX TO PART II 
This contains very recent measures of neglected stars, and those having considerable relative 
motion, which could not be given in Part II. These observations were principally made at the Lick, 
Flower, and Yerkes Observatories, and include only those of pairs where late positions are important 
to the completeness of this work. 
The Appendix also contains some measures from printed observations which were published 
after a portion of Part II was in type These include the first part of Doolittle's measures in 
Publications of the Flower Observatory, Vol. II, and a few measures by Biesbroeck, Espin and others. 
