Old Time Nautical Instruments Classic Reprint

Author : Harvard College Observatory
Publisher : Forgotten Books
ISBN 13 : 9780656312092
Total Pages : 20 pages
Book Rating : 4.3/5 (12 download)

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Download or read book Standard Public Time (Classic Reprint) written by Harvard College Observatory and published by Forgotten Books. This book was released on 2018-02-11 with total page 20 pages. Available in PDF, EPUB and Kindle. Book excerpt: Excerpt from Standard Public Time The method ordinarily used by the jewellers and amateurs is inexact. With a transit instrument, mounted on top of his house, or in some convenient Spot in his yard, and provided with.his ebro nometer and nautical almanac, the observer takes his position on the first clear night, to bring his instrument into the meridian. He Singles out Polaris by means of the two pointers in the Dipper, and, pointing his telescope so that Polaris is bisected in its field of view by the middle micrometer wire, he keeps Polaris steadily on the wire, by moving the instrument bodily until the chronometer denotes the time of the star's transit. With very little regard for the exact levelling of the horizontal axis of the transit, he then aligns a mark of some kind in the meridian, and waits until the next noon-day sun shall give him the Opportunity of determining his chronometer error with the mininum of computation. This method can never be adequate, either for the regu lation of the better grades of clocks and watches or for furnishing the public time; for our standard of time like our standards of weights and measures, should be exact. In using the transit instrument in this manner. The jeweller assumes, first, that the east and west axis is truly horizontal; second, that its bearings are perfectly symmetrical, and symmetrically placed third, that the line of collimation of the telescope coincides with a line joining the central point of the micrometer with the optical centre of the object-glass, and also coincides with the meridian; and, fourth, that this line is perpendicular to the east and west axis. Now, in reality, even in the most perfectly constructed instruments of our large observatories, all of these sources of error are assumed to exist; and, with each determination of time, a number of observations are made, having in view the object solely of determining the exact amount of each of these errors and the position of the instrument used. Thus. About the Publisher Forgotten Books publishes hundreds of thousands of rare and classic books. Find more at www.forgottenbooks.com This book is a reproduction of an important historical work. Forgotten Books uses state-of-the-art technology to digitally reconstruct the work, preserving the original format whilst repairing imperfections present in the aged copy. In rare cases, an imperfection in the original, such as a blemish or missing page, may be replicated in our edition. We do, however, repair the vast majority of imperfections successfully; any imperfections that remain are intentionally left to preserve the state of such historical works.