262 Mr, Bowditch on the Longitude of Cambridge. 
ed there by astronomers in an interval of clear weather. This obser- 
vation being made under such unfavourable circu mstances, and mak- 
ing the longitudes nearly 20 seconds less than-the other observations, 
it was thought proper not to take it into the computation, and as no 
other observations were known, that could be used in this calculation, 
the mean of the preceding values was taken as the true longitude of 
Cambridge. . 
‘Solar Jigs aes 5,1766. (2Obs.Green. 20bs. Camb.) 4h, 44/30" 6 
June 24,1778. (2O0bs.Green. 2 Ohs. Chelsea.) 28 0 
April3,1794.(2Obs.Paris, 2Obs.Green, 4 Obs.Camb.) Bi 4 
June 16, 1806. (Several in Europe, 4 Obs, in Salem.) 24 9 
‘Transit of Mereury—Nov. 5, 1743. (4 Obs. Paris, 2 Obs. Camb.) 32 3 
Transit of Venus-—J une 354769, (2Green. 4 Paris, 1Camb,41 Newbury.) 31 4 
: Mean of above thirty observations 4 44 29 7 
As the difference of latitude of Cambridge and Salem was found 
by a trigonometrical survey to be less than by astronomical observa- 
tions, it was thought proper to estimate the effect of a supposed error 
in the latitude of Salem, Cambridge or Chelsea. To do this the pre- 
ceding calculations were repeated with latitudes increased by one min- 
ute, and it was found that the longitudes, deduced from the observa- 
tions of 1806, 1743 and 1769, were not varied a tenth of a second by 
this change, and the corrections of the observations of 1766, 1778, 
and 1791, were respectively — 1”*5 + 12+ 1'°8, therefore the mean 
longitude just found would be increased 1 of a second by an increase 
of L minute in the latitude of Cambridge, consequently the error in 
the longitude, arising from this source, must be wholly insensible, 
since there cannot be an error of'a minute in the latitude of that place- 
‘Hence the difference of meridians between Harvard Hall in Cam- 
bridge and the Royal Observatory of Greenwich may be assumed 28 
equal to 4h, 44’ 297, and from the near agreement of these observa 
