Used to describe both binary systems and optical doubles, the term 'double star' has been familiar to astronomers since the seventeenth century. This book, first published in 1879, outlines the history of their study, and describes the methods and equipment needed in order to observe the fascinating phenomenon. Written for non-specialists by Fellows of the Royal Society Edward Crossley (1841-1904), Joseph Gledhill (1837-1906) and James M. Wilson (1836-1931), the catalogue of over 1,200 double stars appears beside detailed notes and does not assume mathematical expertise. Also offered are a fully worked example of how to find the orbit of a binary star, and illustrations of telescopes, observatories, and even custom-made observation chairs. This reissue includes the supplement with corrections and notes published in 1880. A standard reference text in the late nineteenth century, the work remains a resources for students and scholars of the history of astronomy.