An account of the methods used to describe lines, on Dr. Halley's chart of the terraqueous globe ; shewing the variation of the magnetic needle about the year 1756, in all the known seas ; their application and use in correcting the longitude at sea ; with some occasional observations relating thereto / [William Mountaine].

  • Mountaine, William, active 1736-1778.
Date:
[1757]
Catalogue details

Licence: Public Domain Mark

Credit: An account of the methods used to describe lines, on Dr. Halley's chart of the terraqueous globe ; shewing the variation of the magnetic needle about the year 1756, in all the known seas ; their application and use in correcting the longitude at sea ; with some occasional observations relating thereto / [William Mountaine]. Source: Wellcome Collection.

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    [ >3 ] Places, made alfo on Shore; and of the Diredlion and Velocity of Currents, &V. When a Ship comes into Port, let the Difference of Longitude between the Place failed from, and the Port arrived at, according to every particular Man’s Account, as well as by the Ship’s Jour¬ nal, be entered therein. Where feveral Ships fail together, fuppofe the Admiral or Commodore was to fummon all the Captains as often as Weather, 0?r. will permit, and in this Meeting that all the particular Ships Journals were produced and compared ; in order therefrom, to form a Fleets Journal, in the fame manner as before. Suppofe again, that thefe Ships and Fleets Journals, and all other Accounts relating to this Subjedl that fhould come to Hand by this, or any other more convenient and pradlicable Method that may be hit upon, were examined at proper Periods, by Per- fons appointed for that Purpofe; might not more accurate Charts be made from them, than any Extant ? Might not the Variation,* Currents, be fo far accounted for in moft Parts of the World, as to render the Bufinefs of Navigation much lefs uncertain and hazardous than at prefent; and would not fuch a Knowledge of the Variation as he has been obferv’d before, even pra&ically deter¬ mine the Longitude at Sea ? Of this material Truth, the eminent and ingenious Mr. Edward Wright, (Inventor of the Charts commonly, tho’ falfely, called Mer¬ cator'^) was well apprized, many Years ago, as may be feen in his Book, entitled, Errors in Navigation detected and corrected. Second Edition, and alfo in the Third, printed Anno 1657, by Jofeph Moxon\ in the Appendix to which called the Haven’■finding Art, he expreffes himfelf thus, viz. 44 The Vaiiation of the magnetical “ Needle, and the Latitude of the Place being known, the fame “ Place may be found, although the Longitude be unknown, 16 and that daily Experience plentifully teacheth, &c. And again, 44 neither is this unworthy the marking which hath “ often happened, that he which fhould have failed to the Ifle of St. Helena, when he was come to the Latitude of the fame IQand, 44 and Taw not there the lfland, and was alfo ignorant whether he “ were to the Eaftwardor Weftward from the fame,, by Conjec- 44 tures fought that Place towards the Ea(f, which indeed lay 44 from him towards the Weft, and fo the further he failed, th e 44 further always he went from that Ifland. Now I leave it ro 44 thy Confideration, if he (whofoever he were that was Mafter of 44 that Ship, which diligently fought that Ifiand for the Space of 44 certain Weeks, tacking about alfo divers Times, before he could ftnd ' u._