INTRODUCTION 
This catalogue in its first form was the result of my own needs soon after acquiring the six- 
inch Clark refractor in 1870. From the beginning that instrument was devoted almost entirely to the 
observation of double stars. Objects were constantly being found which could not be identified in any 
of the books at hand for reference, the principal one being an early edition of Webb's Celestial Objects. 
At this time there were but few books in Chicago bearing upon the subject of double stars. The 
old Dearborn Observatory, then under the directorship of Professor T. H. Safford, had a copy of 
Struve's MensuraeMicrometricae, some incomplete volumes of the Astronomische Nachrichten, and a few 
other works of minor importance. The small refractor showed many pairs, more or less difficult, 
which could not be found recorded in any of the available lists. At that time to make a complete 
catalogue of the then known double stars, it was necessary to first make pen copies of nearly every- 
thing required for this purpose. These were secured by visiting the libraries of the Naval and other 
observatories, and by borrowing the books from various quarters. In this laborious way manuscript 
copies were acquired of the material parts of nearly all publications relating to double stars. These 
copies included Struve's Mensurae Micrometricae, and Positiones Mediae ; the Pulkowa Catalogue; the 
seven catalogues of Herschel II (Memoirs R. A. S.) ; the catalogues of Herschel, and Herschel and 
South (Philosophical Transactions') ; and a great number of minor lists and measures scattered through 
the volumes of the Philosophical Transactions, Memoirs and Monthly Notices of the Royal Astronomical 
Society, Astronomische Nachrichten; and hundreds of society, observatory, and other publications. In 
the course of time original copies of the more important of these works were picked up, and in the 
end a very complete library was formed of substantially everything relating to the known double stars. 
The manuscript general catalogue was kept continuously posted to date by the addition of all new 
stars and new measures from current publications. In order to make room for this new material, a 
second manuscript edition became necessary, and still later a third, which finally passed into the hands 
of the printer, and now appears in printed form. 
The southern limit of 31 declination, adopted at the beginning, has been retained. This 
includes all the stars that can be well seen at the principal northern observatories. But little had been 
done then, and the situation is sensibly the same at this time, in the way of a thorough examination of 
the southern stars, and in the measurment of those previously catalogued by Herschel and others. The 
northern heavens were much better explored when Struve's great work appeared in 1837 tnan tne 
southern portion is now after an interval of seventy years, notwithstanding the labors of Tebbutt, 
Russell, Sellors, See, Innes, and others; and a general catalogue of the known objects at this time would 
be of as little use as a similar work for the northern sky would have been if prepared at the conclusion 
of the researches at Dorpat. It is possible that by the end of the present century, the information 
then given by an examination of the stars to the eighth magnitude, and by the necessary re-measure- 
ment of the old and other known pairs, may make it worth while collecting all the material into a 
single catalogue for reference, provided a few zealous observers shall arise with an undivided interest 
in this special work, and with suitable advantages in the way of telescopes and locations. It would 
have served no useful purpose at the present time to have extended the limits of this catalogue to 
the south pole. All that is needed in this direction at this time has been supplied by Innes who has 
compiled a provisional reference catalogue of the more prominent southern doubles, with measures of 
1898, printed in the Annals of the Royal Observatory, Cape of Good Hope, Vol. II. 
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