The present volume is the first of a projected series having the double purpose of developing the elements of Practical and Theoretical Astronomy for the special student of the subject, and of serving as a handbook of convenient reference for the use of the working astronomer in applying methods and formulae. The plan of the series has been suggested by the authors experience as a teacher at the Johns Hopkins University, and as an investigator. The first has led him to the view that the wants of the student are best subserved by a quite elementary and condensed treatment of the subject, without any attempt to go far into details not admitting of immediate practical application. As an investigator he has frequently been impressed with the amount of time consumed in searching for the formulae and data, even of an elementary kind, which should be, in each case, best adapted to the work in hand.
The most urgent want which the work is intended to supply is that of improved methods of deriving and reducing the positions and proper motions of the fixed stars. Modifications of the older methods are made necessary by the long period, 150 years, through which positions of the stars now have to be reduced, and by the extension of astrometrical and statistical researches to a great and constantly increasing number of telescopic stars.