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A lunars tale from the 1840s
From: Frank Reed
Date: 2008 Mar 21, 06:19 -0400
From: Frank Reed
Date: 2008 Mar 21, 06:19 -0400
From "The Nautical Magazine" 1845, via google books... Under the title, "CHRONOMETERS AND LUNARS," After a preamble offering some revised positions for islands and points in the Indies, the author writes: "I would now beg to offer some remarks relative to chronometers, and the fearful consequences that may arise if we place too much confidence in them, which from their beautiful and improved construction we are now too apt to do, and neglect those observations of the Heavenly bodies (which can only be of use by their being in constant practice) when you may have confidence in them. On my outward voyage, I had a beautiful watch of Murray's, which differed only nine seconds, in my run from Portsmouth to the Great Ladrone (on the coast of China). I placed great reliance on this watch during my homeward voyage, after leaving the coast of Java, and as soon as the moon came in distance I obtained a few sets of sights which gave the watch a considerable error, nearly three inmutes. At this time I imagined my distances must have been incorrect, but the day previous to getting on the L'Agulhas bank, and in a run of about thirty days from Java Head, I was fortunate enough to get the mean of some thirty or forty distances, and I was much astonished that they gave the watch an error of ninety miles to the westward. I also carefully observed the sun's semi-diameter, and this corresponding with the Nautical Almanac, gave me confidence in my sights, and shook my confidence in the chronometers. It also fortunately placed me on my guard, and as on rounding the land, I was in a position to make Cape L'Agulhas at daylight I did not bear away. I was running nine knots at the time, with a strong S.S.W. wind, and did not see the Cape until 2 P.M., having run since daylight about 80 miles departure, which made the lunar sights as near correct as I could take the bearings of the land, at about four leagues distance in hazy weather. Had I been by chronometer, near the longitude of the Cape in the evening, I certainly should have borne away before morning, and had I done so, the melancholy fate of the ship which I commanded would, I fear, have been similar to the Arniston, Northumberland, and various others. How to account for this error in the watch has quite bewildered me, excepting it arose from magnetic attraction, as from some cause or carelessness a brace of pistols was placed close to the watches, which I had removed, directly I found the watches had altered their rates. The chronometer has since remained stationary, and retains the same rate as when I was off the Cape. On my passage towards England, after rounding the Cape, I took every opportunity of obtaining lunar distances ; and two days before I reached St. Helena, I spoke a ship which had also seen Cape L'Agulhas, and we differed seventy miles in our longitude. This startled me. But when I found my brother mariner had not taken any lunar sights, and having confidence in my instrument, I steered boldly for the island, and made it ahead about an hour before daylight. I was at St. Helena two days. Each day I got the Greenwich time from the observatory, and in taking the mean of my lunars about 100 distances, I was much pleased to find we only differed one second from each other. I would from these circumstances caution mariners, not to be too confident in their chronometers, and to lose no opportunity of obtaining lunar observations when practicable, and which I fear is now too much neglected, and which unless they are constantly practised can be of little avail, and can give no confidence to the observer. I have generally rated my chronometers by lunars, and have hitherto been fortunately correct in doing so, as they seldom retain the rate given by their constructors, and having two sextants, one of which being Troughton's, which as an instrument of confidence for navigation, is worth to me all the chronometers that were ever constructed. I have once before made some small contribution to your work, and am a subscriber from its commencement, and many an agreeable hour, I spend at sea in conning over its pages. Should yon think this worth inserting, or any part of it in your publication, I beg you will do so. I have the honour, &c., T. N. WERE, Commander of the Ship City of Derry. " Some good stuff in there from the final decade of lunars... -FER --~--~---------~--~----~------------~-------~--~----~ Navigation List archive: www.fer3.com/arc To post, email NavList@fer3.com To , email NavList-@fer3.com -~----------~----~----~----~------~----~------~--~---