THE COMPASSES OF IRON SHIPS.

Grey River Argus, Issue 55, 19 May 1866, Page 3

THE COMPASSES OF IRON SHIPS.

W From the Times. ) gin the course of last autumn a correspondence took place between the Hyclro|raphic Department of the Admiralty, the president of the Royal Society, and the Board of Trade, on the subject of the Kiriation of tho compasses of iron ships. Ellis correspondence was towards the close" If the year forwarded te the Committee of ■Lloyd's Register, and has just been printed find circulated under their auspices among the owners of that class of vessels. It Rpens with a letter from Staff-Commander i?. J. Evans, R.N., Chief Naval Assistant Mn charge of the Magnetic Department mndev the Hydrographer of the Admiia'ty, « wliich, after briefly adverting to the »iective. character of the compasses emin the Royal Navy previous to PKS7, and the appointment of a Committee ■of Officers conversant with magnetic inIstruments to inquire into a state of things ■wliich had been found to be so. pregnant ■with mischief, he points out that the result j ■of the investigation had been not only the ■improvement of the compass itself, but the ■establishment on board men-of-war of a ■system of compass adjustment which con--1 turned in operation up to the present time, &and which proved to be very advantageous. ■The principal feature of this system he •describes as being the having in eaCliship ■a standard compass distinct from the steer■ing compass, fixed in a position, selected, Miot for the convenience of the helmsman, ■but because of the moderate and imif orm Bxmouht of deviation observable, and the each ship to-be -swung, and to be jMiavigated by a table of errors. To the Mieglect of the use of a standard compass ]Hie attributes many of the disasters which ]Hiave overtaken merchant vessels, and iHherefore strongly recommends that the (■•.mployment of an instrument so simple in ißfcself , and in practice so secure, should, as fHar as possible, be enforced. Assuming t^Bhat some such system: will eventually be a^^Wopted in the merchant service, Comn^fcinder Evans, in an appendix to his L^Hter, offers certain suggestions which he t:^^Hiks might be found to be of considera'^^Hp practical xitility. He would have, so ft^^Hasthe requirements of a slup would p^^Hnit, special arrangements made in the ct^^^vse of her construction to provide a si^^Hfible place for the compass, wliich slfl^Vpd be fixed at such a height as to. comr^^H^l a clear view of the . horizon above j c '^^Bl>vilwarks. and to be out of .the wf^o^

the' sails j while care should taken that at least ten feet should intervene between it • and any elongated mass of iron. ■ He also recommends that every iron slu'p after being launched should, to as great an extent as was practicable, be kept in a position opposite to that which she occupied while on the building slij), observing that when arrangements are made for placing the compass in the after part of, a vessel, building her with her head to the north would produce exaggerated errors, both when upright and heeling. For many years, it appears, the formation of a table of errors by the process of swinging a ship — a place to fix the standard compass having in the first instance been duly selected — was found to answer tho purposes of the Admiralty in those cases in wMch the, deviations happened to be moderate in amount, In several of the ■ iron vessels whicli.have been recently constructed, however, the extent of deviation lias been so great that magnets had to be ! ' employed with a ..view to its reduction. ] TMs mode of correction— perfect though it may be-— has not at the same time been allowed to supersedo in our navy the system of obtaining a table of errrors, and navigating the. ship by that table. The benefits, wMcli ori the score of safety have accrued to the navy in consequence of tlie adoption by tlie Admiralty of the plan wMcli he • thus sketches, Commander Evans thinks cannot be over-estimated, and he points' out, in proof of its efficiency, that the "Admiralty standard compass," which lias, with but little modification, stood tlie test of 25 years' use, has been copied in every country where attention has been directed to the subject with- winch. Ms letter deals. He adds that in the manufacture of compasses for the mercantile marine much expense is at present incurred for purposes of mere ornament, and is of opinion that considerable advantage would be tlie result if a model comp&s* of sufficient delicacy and accuracy could be fixed upon and furnished at a moderate price. That being done it would, of course, be necessary to secure the.services of a sufficient number of persons competent to perform the work of adjustment, and also to determine the time at which the adjustment should be examined. In dealing with these points Commander Evans observes that several persons were to be found at some of our great mercantile ports who, without having any clear knowledge of the principles of magnetism, were yet, from constant practice, skilful adjustors of -compasses, and suggests that the registration of the names of such men might be desirable as a preliminary step. As to the periods for examining the adjustments, he ia of opinion that the following recommendation of the Liverpool courpass committee fully meets, the difficulties of the case : — " There appears sufficient reason for reqiiiring that a new iron sailing ship or steamer should be' swung immediately before each of the first two ortM-ee voyages; that all iron vessels should be swung immediately before the first voyage, following any considerable amount of repair, whenever a change has been made in the p >sition of the standard compass, whenever tJiere is a change of captain, unless the new captain had cliarge of the vessel dining the preceding voyage as chief officer." Commander Evans, concludes by remarking that the present state and prospects of the science and practice of the correction of the compass render it impossible to ofl'er - with- confidence any -complete set of suggestions as to the system to be adopted in the mercantile marine.