Getting From Here To
p. 97 · Read in the full issue
There At Sea
Whether you are a deck-chair sailor, a professional, or an ocean yachtsman, Frank Knight, Extra Master Mariner, has something for you in “A Guide to Ocean Navigation”.
The title suggests a text book, and therefore a book to be read by those who wish to practise navigation. But this is no text book in the true sense of the word.
It is a book about navigation which traces its historical development from the early Mediterranean era until the present day.
Navigation to many people means mathematics—especially trigonometry. In a book of 174 pages the author covers his survey of celestial navigation in 130 pages and of these mathematics is found on about 10 pages only. The layman would lose nothing if he skipped the calculations and continued reading. For those who are interested, however, the author has included a chapter on trigonometry.
The book commences with a description of the navigational techniques em ployed by the Ancients and leads on to the development of the compass. How latitude was first found by observation of the sun and stars is discussed, and the methods used today will be clearly understood even by those readers whose mathematical knowledge does not go beyond the multiplication tables.
The determination of longitude was unknown to the early navigators although the problem was understood. And the problem was one of time.
In 24 hours, as the author explains, the earth spins through 360 deg., or 15 deg. per hour. Suppose the sun, as seen from a ship, was highest in the sky (noon) three hours after it was highest as observed from Greenwich. The ship would be 45 deg. further west than Greenwich.
The reviewer has here oversimplified the author’s account but, nevertheless, it illustrates the problem—the necessity for a most reliable timekeeper so that local observations of the sun and stars could be related to Greenwich.
The invention of the chronometer solved the problem and this instrument is still of fundamental importance to the navigator.
A chapter on Radio Aids to Navigation, a typical set of calculations made by a navigator (all carefully explained), and an excellent glossary of navigational terms, complete the book. The whole is well indexed and Illustrated.
The author makes one mistake, though, when he states that the length of a true solar day varies from 23 hours 44 minutes to 24 hours 14 minutes —the maxi mum variation from the mean length of 24 hours is only 30 seconds. He also ex presses the opinion that the air navigator, who uses radio aids to a much greater extent than his marine counterpart, “should be able to find his way home by the sun or stars as a last resort”. Qantas Airways demand that their navigators fix position by stars every 40 minutes —certainly not a last resort!
As a reviewer with similar background and qualifications as the author I can recommend this book to the layman or professional whether they seek enlighten ment or enjoyment, or both. —W. D. HEIGHWAY. (A GUIDE TO OCEAN NAVIGATION. Published by Macmillan and Co. Aus tralian price, 29/9.)