IN ITS RELATION TO PRACTICAL NAVIGATION BY CHARLES LANE POOR Professor of Astronomy in Columbia University; Author of "The ILLUSTRATED G. P. PUTNAM'S SONS PREFACE HIS work is intended for the general reader THIS as well as for the practical navigator. It is an attempt to explain in non-technical language and without the use of complicated mathematical formulas the fundamental facts and principles that form the basis of all navigational methods. Navigation is founded upon Astronomy, but it is not essential for the navigator, in order to find his way from port to port, to know the methods by which the size, the shape, and the motions of the earth are determined, and to be familiar with the physical characteristics of the sun and stars. A knowledge of these astronomical facts is, however, necessary to those who wish to be thoroughly posted in the science of navigation. Every navigator knows how to use the data found in the Nautical Almanac, but few have the slightest idea how these data are collected and made available for the immediate needs of the practical sailor. The Sumner method of finding one's position at sea is fundamental and, when combined with modern methods of reduction, is most simple and readily applied to all navigational problems. 304590 The time-honoured noon sight for latitude and the morning or afternoon sight for longitude are but special cases of this most powerful method. The theory of the Sumner lines of position is so easy to understand, and at the same time it is so widely applicable, that it is made the basis upon which the whole theory of practical navigation depends. At the end of each chapter is to be found a sort of appendix containing notes, formulas, and practical examples. This portion of the book forms a condensed treatise on modern methods of navigation. A considerable portion of the book is devoted to an explanation of the tides and tidal currents; their peculiarities and their causes. That the tides are caused by the attraction of the sun and moon is well known, but just how this attraction causes the radically different tides in different portions of the earth is not fully realised. Until very recently the ablest investigators considered the tides as world phenomena, the tides in each bay and ocean as a part of one great tidal wave which sweeps around the entire world. To-day the able researches of Dr. Harris have shown us that the tides and tidal currents are essentially local phenomena, that the tides of each ocean basin are practically independent of those of the rest of the world. Without the hearty co-operation and assistance of the Coast and Geodetic Survey this portion of the book could never have been put into |