A voyage towards the North pole undertaken by His Majesty's command, 1773 . , made by Dollond; and fometimes by* Captain Phipps, with a fraaller of four inches radius, made by Ramfden, which commonly agreed with the* other within a minute. The error of the fextant was o-enerally found by obferving the diameter of the Sun; which if the fame as double the femidiameter fet down in the Nautical Almanac, fliewed that the inftrument was perfedly adjufted; if it differed, the< difference was the error of the fextant. It was necef-* fary to know this error of adjuftment very exactly,* and therefore
A voyage towards the North pole undertaken by His Majesty's command, 1773 . , made by Dollond; and fometimes by* Captain Phipps, with a fraaller of four inches radius, made by Ramfden, which commonly agreed with the* other within a minute. The error of the fextant was o-enerally found by obferving the diameter of the Sun; which if the fame as double the femidiameter fet down in the Nautical Almanac, fliewed that the inftrument was perfedly adjufted; if it differed, the< difference was the error of the fextant. It was necef-* fary to know this error of adjuftment very exactly,* and therefore I generally repeated the obfervation of the Suns diameter feveral times, and from the mean of the refult found the error of tjie fextant. This error will equally affeO: all the obfervations taken near* the fame time, and therefore cannot be difcovered* from the comparifon of feveral obfervations. Under< the equator, an error of one minute in altitude, near the prime vertical, will only produce an error of-* four feconds in the apparent time; but in the latitude of /7. 222 APPENDIX. Accouwr of the Astronomical Observations andTime-Keepers, by Mr. Lyons. « nr^ H E obfervations for finding the time at fea, wese -*- taken with a brafs Hadleys Sextant of eighteen inches radius, made by Dollond; and fometimes by Captain Phipps, with a fraaller of four inches radius, made by Ramfden, which commonly agreed with the* other within a minute. The error of the fextant was generally found by obferving the diameter of theSun; which if the fame as double the femidiameter fet down in the Nautical Almanac, fhewed that the inftrument was perfedlly adjufted; if it differed, the difference was the error of the fextant. It was necef-* fary to know this error of adjuftment very exadly,* and therefore I generally repeated the obfervation of the Suns diameter feveral times, and from the mean of the refult found the error of t}ie fextant. This error will equally affeQ: all the obfervations taken ne
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