INTRODUCTION 
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The measures which follow were made with the 40-inch refractor of the Yerkes Observa¬ 
tory in the years 1907 to 1912. The mean results of prior measures with the same instrument in 
1897 to 1906 are given in the General Catalogue of Double Stars (Carnegie Institution of Wash¬ 
ington, 1906). These observations have been made in the usual way, fully described heretofore; 
and, as far as possible, each star has been measured on at least three nights. The most probable 
value of one revolution of the micrometer-screw, as found from a large number of observations, 
is 9 " 666 ; and this value has been used throughout the work at the Yerkes Observatory. 
The larger number of stars selected for measurement, given as Part II of this volume, are 
taken from the General Catalogue of Double Stars for reasons which will generally be apparent 
from the notes and observations cited in that work. By far the greater number of stars given in 
the General Catalogue as having proper motion are not included here, because the obser¬ 
vations there cited are of recent date and further measures are not needed at this time. Many 
hundred examples of proper motion stars of this kind will be found there, and in that respect 
this work is supplementary to the General Catalogue. 
The other list, forming Part I, includes all other stars for which prior observations with the 
micrometer have been made. Unfortunately the early work in this field is confined to a few 
observers, the principal ones being Otto Struve, Engelhardt, and Ball. For some of the other 
stars recent photographic positions have been found, but in most cases the time-interval is too 
short to give a very accurate value of the relative change. This objection will be removed by 
observations to be made hereafter. 
The small stars from Zone 26° of the Oxford Astrographic Catalogue are taken from a 
list prepared by Mr. G. H. Plamilton of the University Observatory. This list gives the place, 
proper motion, and photographic magnitude of some fifty stars, principally below the magni¬ 
tude limit in Argelander, from plates taken for the most part in 1907 and 1908, the proper 
motions being derived from a comparison with other plates made a few years earlier. All of 
these were put on the observing-list and, as far as possible, compared with one or more fainter 
stars in the field. In a few instances there were no comparison stars within the range of the 
micrometer. 
Boss (Astronomical Journal, 604) has called attention to a group of thirty-nine bright 
stars, principally in Taurus, which appear to have a common proper motion of approximately 
of'10 in the general direction of about ioo°. These stars were placed on the observing-list, and 
nearly all of them connected with faint stars in the field for verification of the proper motions 
given from meridian positions. I have noted three other stars, overlooked by Boss, which evi¬ 
dently belong to the group. They are 37 Tauri, 55 Tauri (OS79) and 0^82. 
When there are prior measures of any of the comparison stars observed here which seem 
to warrant a conclusion as to the movement of the proper motion star, the result is given and 
compared with former values derived from observations with the meridian circle. When the 
proper motion is small, say a tenth of a second of arc or less, the separate determinations from 
meridian positions by the leading authorities on this subject are apt to be discordant and incon- 
iii 
2924 H 2 
