Remarks on a pamphlet [respecting H.'s chronometer] lately published by the Rev. Mr. Maskelyne, under the authority of the Board of Longitude / By John Harrison.

  • John Harrison
Date:
1767
Catalogue details

Licence: Public Domain Mark

Credit: Remarks on a pamphlet [respecting H.'s chronometer] lately published by the Rev. Mr. Maskelyne, under the authority of the Board of Longitude / By John Harrison. Source: Wellcome Collection.

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    pend upon Obfervations of the Moon and Stars, and upon a Watch to keep Time, from the laft Solar Obfervation with fuffi- cient Exactnefs, which common Watches cannot be depended upon to do ; well there¬ fore might Mr. Maskelyne admit that my Invention would become of confiderable Value, even if taken in Aid of the Lunar Tables. I leave the Reader to judge of the Practicability of making thefe Obfervations from what follows; To afcertain the Longitude by the Moon and a Star, requires a didinCI Horizon to be feen in the Night, which is next to impoffi- ble, and if you have not an Horizon, the Altitude of neither Moon nor Star can be taken : It alfo requires (and this perhaps when a Ship is in a high Sea) the Diflance of the Moon and Star, in order to come .at which, the Image of one of them mull be refle&ed through a filvered Glafs, and the other feen through an unfilvered Part of the fame Glafs; and they muff be brought into Conjunction in the Line that connects the filvered and unfilvered Parts, and this to an JExaCinefs only true in Theory, for an Error of a Minute of a Degree committed in this Obfervation, will miflead the Mariner Half a Degree in his Longitude ; Now I call up¬ on any Aftronomers of Reputation publick- ]y to declare, that they have, even at Land, and with the bed Inftruments Europe affords, been able to make this Obfervation of the Moon and a Star with any thing like the Pre- the Longitude within ciiion required to determine