THE rapid advance in the cultivation of Practical Astronomy which has recently been made in the United States is one of the most encouraging features of the age. It is less than twenty-five years since the first refracting telescope, exceeding those of a portable size, was imported into the United States, and the introduction of meridional instruments of the large class is of still more recent date. "We may now boast of two Observatories, liberally equipped with instruments of the best class, and provided with a permanent corps of observers, as also a considerable number of other establishments more or less complete, and a still larger number of telescopes of dimensions adequate to be employed in original research...

THE great progress of astronomical discovery, during the *ast few years, has induced the author of this work to prepare, with much labor and expense, a new edition, which should fully exhibit the features of the science in their latest physiognomy. Since the stereotype edition was first published, in 1844, numerous and important discoveries have been made, both in the solar system and among the fixed stars. The dimensions of the planetary system have been nearly doubled by the addition of the planet Neptune ; the number of the Asteroids has been increased from four to twenty-seven ; interesting discoveries have been made in the Rings of Saturn, and an eighth member has been added to his retinue of satellites ; and the subject of Comets has received a new impulse by the appearance of the remarkable cornet of 1843...

An attempt has been made in these pages to trace the evolution of intellectual thought in the progress of astronomical discovery, and,by recognising the different points of view of the different ages, to give due credit even to the ancients. No one can expect, in a history of astronomy of limited size, to find a treatise on "practical" or on "theoretical astronomy," nor a complete "descriptive astronomy," and still less a book on "speculative astronomy." Something of each of these is essential, however, for tracing the progress of thought and knowledge which it is the object of this History to describe...

THE chief authority for the Life of Sir William Herschel is Mrs. John Herschel's " Memoir of Caroline Herschel " (London, 1876). It embodies Caroline's Journals and Recollections, the accuracy of which is above suspicion. William himself, indeed, referred to her for dates connected with his early life. The collateral sources of information are few and meagre ; they yield mere gleanings, yet gleanings worth collecting. Professor E. S. Holden has had recourse to many of them for his excellent little monograph entitled "Herschel, his Life and Works" (London, 1881), which is usefully supplemented by "A Synopsis of the Scientific Writings of Sir William Herschel," prepared by the same author with the aid of Professor Hastings...

FOR a full explanation of the circumstances in virtue of which the matter forming the contents of this volume now appears dissociated from that to which it was joined in the first three editions of this work the reader is referred to Vol. I. of the 4th edition, published in September, 1889. Suffice it therefore now to state briefly what has been done to render the contents of this volume as acceptable as possible to the public.

PT^HE remarks which appear in the Preface to the Third Edition (see post] apply almost word for word, so far as they go, to the Fourth Edition. Yet it is necessary for me to write an independent Preface in order to call attention to the altered circumstances under which this work is now presented to the reader. If the development of Astronomy between 1867 and 1877 was great, its development between 1877 and 1889 has been still greater. And besides this, there were important omissions in the ground-plan of the book which I have long been very desirous of making good, whenever time or opportunity became available.

THERE is bat little alteration in this edition, for so far as regards the older astronomers at all events there has been nothing to add or to correct. It may, however, be mentioned here that a commemorative tablet has recently been placed on the house, in New King Street, Bath, in which William Herschel resided. Nor could it be possible to allow the sketch of the late Earl of Eosse to be reprinted without adding the fact that his youngest son, Hon. C. A. Parsons, is, as all the world knows, the famous engineer who invented the steam turbine.

THE rapid progress of the science of astronomy, for the liwr. "few years, has again rendered it necessary to revise the Geography of the Heavens a work, the popularity of which is sufficiently proved by a sale of 300,000 copies. The editor has, therefore, availed himself of the occasion to make such improvements, both in the book and maps, as seemed to be demanded by the progress of the science, and the most approved methods of instruction.