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Longtitude of the 1si. Meridian of the Survey. 
Tur methods resorted to for determining longitudes being rather less 
susceptible of accuracy than those for determining the latitude, it has been 
deemed adviseable to reduce all the observations, made for the former pur- 
pose, to one point. Having thus obtained a mean result, the differences of 
longitude of the various places of the survey being applied to it, their 
absolute longitude from Greenwich becomes known, 
Ir is not our purpose here to enter into any comparison of the relative 
degrees of value, which the several methods of determining this pomt may 
possess. It may be sufficient to state, that finding in practice, the immer- 
sions and emersions of Jupiter’s satellites, as compared with the nautical 
almanack, afforded: us very close results, and being in possession of instru- 
ments fully equal to such a course of observations, we have naturally 
leaned to them, not omitting however any opportunity, when in a con- 
venient place, of making also other observations. It would be no doubt 
desirable that these should be compared with others made at a place, the 
longitude of which is well known. This however cannot be Greenwick, 
because the number of immersions and emersions visible both m this: coun- 
try and at Greenwich is very small, and of these, few can be observed at 
that place, owing to the uncertain climate. Madras therefore naturally 
presented itself as more properly adapted to this purpose. ‘The seat of an 
observatory of the Honorable Company, its longitude must be known to 
