People constantly talk to each other about experience or knowledge resulting from spatial perception; they describe the size, shape, orientation and position of objects using a wide range of spatial expressions. The semantic treatment of such expressions presents particular challenges for natural language processing. The meaning representation used must be capable of distinguishing between fine-grained sense differences and ambiguities grounded in our experience and perceptual structure. While there have been many different approaches to the representation and processing of spatial expressions, most computational characterisations have been restricted to particularly narrow problem domains. The chapters in the present volume reflect a commitment to the development of cognitively informed computational treatments of spatial language and spatial representation. Therefore the chapters present computational work, empirical work, or a combination of both. The book will appeal to all those interested in spatial language and spatial representation, whether they work in artificial intelligence, cognitive science, cognitive psychology or linguistics.

People constantly talk to each other about experience or knowledge resulting from spatial perception; they describe the size, shape, orientation and position of objects using a wide range of spatial expressions. The semantic treatment of such expressions presents particular challenges for natural language processing. The meaning representation used must be capable of distinguishing between fine-grained sense differences and ambiguities grounded in our experience and perceptual structure. While there have been many different approaches to the representation and processing of spatial expressions, most computational characterisations have been restricted to particularly narrow problem domains. The chapters in the present volume reflect a commitment to the development of cognitively informed computational treatments of spatial language and spatial representation. Therefore the chapters present computational work, empirical work, or a combination of both. The book will appeal to all those interested in spatial language and spatial representation, whether they work in artificial intelligence, cognitive science, cognitive psychology or linguistics.

The Grade 11 Learners Book offers the following beniifits. Cover the requirements of the CAPS document for the subject in detail. Facts and concepts are presented in simple, accessible language . Carefully chosen illustrations support the content. New and less familiar words are explained in the glossary boxes on the page. Flow diagrams and study maps are provided at the beginning and end of each section to facilitate understanding of conent , and to be used as a study tool. A glossary of term and concerpts is provided at the end.

METEORS BY CHARLES P. OLIVIER ASSOCIATE PROFESSOR OFXSf RONOMY AT THE UNIVERSITY OP VIRGINIA AND ASTRONOMER AT THE LEANDEB McCoRMicK OBSERVATOBY BALTIMORE WILLIAMS WILKINS COMPANY 1925 COPYRIGHT, 1925 WILLIAMS WILKINS COMPANY Made in United States of America Published March, 1925 COMPOSED AND PRINTED AT THE WAVERLY PRESS TUB WlLMAMB WlLKINR COMPANY BALTJMORB, Mn., U. 8. A. THE GIIEAT BOLIDE OF SEPTEMBER 12, 1923 Photographed by Josef Kleposta, at 21 h 55 m 25 8 G. M. T., at Prague Observa tory. TO THE MEMORY OF MY FATHER GEORGE WYTHE OLIVIER THIS BOOK IS DEDICATED PREFACE One of the few departments of astronomy that has not been brought up to date in a recent book is that dealing with meteors. An excel lent book on meteorites, by 0. C. Farrington, was published in 1915, and during the past few years several important researches on meteors proper have appeared, but no general work on meteoric astronomy has been published since 1871. Such a book, however, is urgently needed, because much of the most valuable recent work on this subject has appeared in foreign periodicals inaccessible to the average reader. In this book many of the most important of these articles are briefly reviewed, and numerous references are given enabling the reader to follow up the subject, if he so desires. The more mathematical and theoretical sections have been segregated and may be omitted without destroying the continuity of the book as a whole for general reading and reference. Practical examples, given in detail, are added for the use of the amateur who may wish to compute his own orbits. As Schiaparellis classical work Sternschnuppen is now very difficult to obtain, and has never appeared in either anEnglish or French edition, many sections of it have been adopted. The methods for computing orbits are taken almost unchanged from the publications of Lehmann-Filhes. The method for computing real heights, due to Schaeberle, is reproduced from one of the Lick Observatory publica tions, with the kind permission of Director W. W. Campbell. Acknowledgment is here made for all the above material. The writer accepts full responsibility for all opinions and criticisms which appear, unless definite references are made to others. It is only fair to state this fact since his opinions, particularly upon radiants and the interpretation of observations, differ radically in certain respects from those of others who have done important work in meteoric astronomy. Further it is clearly to be understood that the opinions here expressed supersede any formerly published by him, as in more than one phase of the subject longer study and experience have caused him very considerably to modify those previously held. And these in turn are, of course, liable to further vii Vlll PREFACE change since, in a subject like meteoric astronomy, few opinions can be final. Most grateful acknowledgment is due to the Superintendent of the United States Naval Observatory, Captain E. T. Pollock, for kindly placing at the writers disposal the facilities of the splendid library of that institution. The preparation of this book would have been impossible without the use of this library, where most of the actual writing was done, while on leave of absence from the University of Virginia. The writer is further under great obliga tions to the following gentlemen for advice and assistance, especially in reading various parts of themanuscript Prof. W. S. Eichelberger, Prof. A. Hall, Prof. G. A. Hill, Dr. W. D. Horigan, Dr. W. J. Hum phreys, Prof. F. B. Littell, Dr. Geo. P. Merrill, Dr. H. R. Morgan, Mr. G. H. Peters, Dr. Thomas L. Watson, Mr. C. B. Watts, and Mr. J. D. Wise. Further grateful acknowledgments are due to Prof. Edwin B. Frost, Mr. L. E. Jewell, Prof. Josef Klepesta, Dr. W. J. S. Lockyer, Dr. Geo. P. Merrill, Dr. Thomas L. Watson, The Astrophysical Journal, the Lick Observatory, Mt. Wilson Observa tory, and Yerkes Observatory for the use of illustrations...