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 pecial 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 author's 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 present volume originated in a desire to present, in small compass, a record of the marvellous progress in astronomy during the past hundred years. Indebtedness should be acknowledged to the valuable works of Professor Newcomb, Professor Schiaparelli, Professor Lowell, Professor Young, Sir Robert Ball, Mr Gore, M. Flammarion, and Miss Clerke, who, as the historian of modern astronomy, occupies a place at once authoritative and unique.

THE following work is translated and abridged from M. Flammarion's LJ 'Atmosphere, Paris, 1872. That some curtailment of the text of the original work was requisite will be apparent when it is stated that the French Edition contains 824 large pages of closely printed matter, and is of more than twice the extent of the present volume. Not only was some compression necessary in order to bring the work within a reasonable compass, but, independently of this, one or two chapters, such as that on the Eespiration and Alimentation of Plants, appeared to have so remote a connection with the subject of the work the Atmosphere that their omission would in any case have been desirable.

SIR WILLIAM ROWAN HAMILTON, the eminent mathematician of Dublin, has, of all writers ancient and modern, most fittingly characterized the ideal science of astronomy as man's golden chain connecting the heavens to the earth, by which we "learn the language and interpret the oracles of the universe."

The oldest of the sciences, astronomy is also the broadest in its relations to human knowledge and the interests of mankind...

THE present volume has been prepared with a double purpose, and upon a plan somewhat unusual. First, an effort has been made to meet the wishes of the rdinary reader who may desire to inform himself as to the present state of astronomic science, or to secure a simple explanation of the many phenomena constantly exhibiting themselves in the universe about him ; and the further purpose has been to produce a satisfactory textbook for use in high schools and colleges.