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One of the earliest series of observations directedto the determination of the moon’s distance was thatundertaken by Lacaille when he visited the Cape of Good Hope in 1750. From a comparison of his re-sults with observations made in Europe , he deducedthe value 57' 13" - 1 for the moon’s mean equatorialhorizontal parallax. This corresponds to a mean dis-tance of 238,096 miles. But it is to be noticed thatLacaille was not acquainted with the true shape of theearth. He supposed the earth’s compression to begreater than it really is; in fact, he supposed theequatorial to exceed the polar diameter in the propor-tion of 201 to 199, whereas in reality the proportion isapproximately 300 to 299; in other words, the com-pression is 3 ^. If this correction is taken into ac-count, Lacaille’s results give for the lunar parallax57' 4" - 6, corresponding to a distance of 238,679 miles.Lalande, by comparing Lacaille’s observations withhis own, made simultaneously at Berlin,* found forthe lunar parallax the value 57' 3"‘7, corresponding'to a distance of 238,749 miles. It will be noticed
meridian. What then is done is to deduce from the observed northpolar distance of the moon when on the meridian at Cape Town i(or from the moon’s place at that time, with respect to someknown star) her position at the moment when she is on themeridian of Greenwich.
* Lacaille was bom on March 15, 1713, and Lalande on July 11,1732, so that Lalande was nineteen years younger than Lacaille,who was himself but a young man when he made his observations.
In fact, Lalande was but nineteen years old when he was sent toBerlin for the purpose of observing the moon simultaneously withLacaille at the Cape of Good Hope .