VOL. LII.] 



FHILOSOPHICAL TRANSACTIONS. 



641 



J which put = k'; and the horary motion of the moon in the ecliptic 



H — 2' 28' 

 W 



D X k' 



60 ~ ' 



The horary motion of the moon in latitude, calling the difference answering 



E X k' 



isK' + 



60' 



to l" increase of the argument of latitude e, is 



The most difficult part in the above computations, and in which a person is 

 most liable to make mistakes, is the computation of the moon's place; but if 

 this be done at land for every 12 hours at least, and the distance of a proper 

 star, or of 2 stars, one to the east, and the other to the west, from the moon's 

 enlightened limb, be computed for every 6 hours at least, according to Mons. 

 De la Caille's proposal, the rest of the computation, which will remain to be 

 done at sea, will be very plain and concise. 



Here follows the series of his determinations of the longitude during his voyage, 

 delivered in an extract of his sea journal. The first column contains the day of 

 the month; the 2d, the latitude; the 3d, the longitude, which he deduced from 

 his observations of the moon, reduced to the nearest noon ; the 4th shows the 

 longitude by account, kept in the usual manner; the 5th gives the difference be- 

 tween the 3d and 4th columns, and expresses how much the longitude deduced 

 from the observation of the moon is west of the longitude by account ; the last 

 column shows whether the distance of the sun from the moon, or distance of 

 what star from the moon, was observed. 



At noon took our departure from the Lizard, which bore full north, distance 21 miles, 

 allowing its longitude from London to be 5" 14' west, and latitude 49^ 57' north 



1761. 

 <J Jan. 20 



(J Feb. 10 

 11 

 15 

 19 

 28 

 9 

 10 

 13 



March 



15 

 17 



18 



19 

 20 



25 



26 



29 



April 6 



I 

 VOL. XI. 



Latitude. 



l6° 

 14 



5 



1 



9 



24 

 25 

 29 



30 

 30 



31 



31 

 32 



49'n. 



3 N. 

 10 ]j. 

 42 N. 



6 s. 



9 s. 

 51 s. 

 49 



39 



37 

 4 



31 

 30 



30 

 7h 



Longitude 

 by reckon- 



27° 



26 



22 



22 



26 



25 



24 



22 



22 

 18 



17 

 15 



23 12 4 5 



51 9 55 4 



32 s. 6 49 w. I 1 



M. came to an anchor in 



the latitude per account 15° 



corrected by observation of 



33'w. 

 47 

 44 

 44 

 2 

 55 

 32 

 19 



58 



7 



27 



57 

 17 

 13 w. 



Longitude by 

 moon w. of 

 account. 



2° 49'w. 



2 35 w. 

 55 w. 

 51 w. 



3 42 w. 



4 12 



5 

 5 36 

 5 25 



4 44 



5 52 



6 7 

 18 47 5 13 



5 46 

 4 34 



4 52 



6 37 

 6 7 



5 58 

 5 36 



the harbour before 

 55' s. longitude by 

 the moon 4° l6' w. 



4N 



The sun or stars whose distance from 

 the moon's enlightened limb was 

 taken. 



Sun's E. limb from moon's w. limb. 

 Sun's E, limb from moon's w. limb. 

 Cor Leonis from moon's w- limb. 

 Pollux from moon's e, limb. 

 Sun's w. limb from moon's e. limb. 

 Aldebaran from moon's w, limb. 

 Aldebaran from moon's w. limb. 

 Sun's E. limb from moon's w. limb. 

 Cor Leonis from moon's w. limb. 

 Cor Leonis from moon's w. limb. 

 Pollux from moon's w. limb. 

 Spica Virginis from moon's w. limb. 

 Pollux from moon's w. limb. 

 Spica Virginis from moon's w. limb. 

 Pollux from moon's w. limb. 

 Pollux from moon's E. limb. 

 Antares from moon's e. limb. 

 Spica Virginis from moon's e. limb. 

 Spica Virginis from moon's e. limb. 

 Sun's w. limb from moon's e. limb. 

 James's fort at St. Helena j making 

 common reckoning 1* 28' £. longitude 



