— 
Mr. Bowditch on the Longitude of Cambridge. 263 
tions Iam inclined to believe that this longitude is more accurately as- 
certained than that of any other place in the United States. The cal- 
culation of President Willard differs about a second from the above 
estimate. Mr. Ferrer in vol. vi. page 359 of the Transactions of 
the American Philosophical Society, computed the longitude by com- 
bining the observations of the solar eclipse of 1791, the transit of Ve- 
nus of 1769, and the transits of Mercury of 1782 and 1789, making 
the longitude greater by 2”*3, but this difference is less than was to 
be expected in using an observation so liable to error as that of the 
transit of Mercury of 1782. 
As several emersions of the first and second cateliites of Jupiter 
have been observed at Cambridge by Professors Winthrop and Wil- 
liams, and published in the Philosophical Transactions and in the 
Memoirs of the American Academy, my curiosity was excited to 
know how near the longitude could be ascertained by comparing 
those observations with the times computed from Delambre’s tables 
of the satellites, published in the third edition of La Lande’s Astron- 
omy. ‘The result of this calculation is in the following table :— 
uP time. ‘Longitude. 
A. “at h. 
Emersion Ist satellite, by Dr. Winthrop, 1768 April 25 913 §2 4.43 33-4 
May 927 37 4 44 25:3 
Fue . 937 25 4 45 02:8 
July 3 945 54 4 44 41°4 
1769 May 14 10 19 07 4 43 09°7 
ug. 23. 7 31 50 4 43 58°1 
Dr. Williams, 1782 July 3 12 09 53 4 44 210 
Aug. 27 9 625 4 44 384 
Sept. 12 73129 4 46 43-0 
Emersion 2d Satellite, by Dr. Winthrop, 1769 June 7 90115 4 44 401 
Dr. Williams, 1782 June 25 9 48 30. 4 44 26°6 
July 12 21 54 4 44 112 
903 49 4 44 27-9 
: Aug. 98 9 03 ° 
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