By the Nautical Almanac, it appears that the Greenwich mean time answering to this distance, must be between 9 P.M. and midnight—the difference of distance answering to this interval of 3 hours, being Lunar dist. at 9 P.M. Greenwich 1°28′52′′ 32 31 16 34 Prop. log. 3065* The difference between the prop. log. at 9 and midnight being 0, the correction of 2nd differences is nothing. Mr. Baily's formula for a lunar observation for longitude is as follows: x the true lunar distance required, * The interval of time past 9 P.M. might of course have been found by a common proportion, without the aid of prop. logarithms. The following example will also show the method of working out a lunar observation, by Dr. Young's formula, all the terms of which are cosines:— Cos M'S' = { 2 cos & (MH + SK + MS) cos 3 (MH+SK – MS) cos M'H cos S'K - cos (M'H+ S'K). MS 95 50 53 cos MH cos SK MH = 35 45 4 ar. comp. cos 0.090678 } The same example, by Mr. Riddle's first method, which will be found in his " Navigation," gives 95° 44′ 29′′ for the corrected lunar distance. By Mrs. Taylor's method, which requires the use of her "Tables," the true distance is obtained as follows: The apparent altitudes and distance are first obtained from those observed, by correcting them for semidiameter and dip if necessary. Then in Table 1 find the log of the corrections for the altitudes on account of the moon's parallax. Trom Table 2 take the logs of the effect of the moon's horizontal parallax upon the distance. moon; also the n in altitude with then, with the cortions as containing id consequently the are found. ons is not available, the same azimuth as distant; the sum or ould then evidently be happened to be one of eenwich time is at once nce as a base, the pro is, that the moon's declinaas an important part of the -ary to know the longitude pt in cases where the moon's octial is nearly a maximum, paratively stationary. Under ay be expected from the last arly on, the prime vertical. N CULMINATING STARS. on causing a difference in the nsit, and that of any star, over ther method of determining the it (or apparent right ascension) of A that of certain stars varying but are calculated for Greenwich mean t tables in the Nautical Almanac. '), and of one or more of these stars, e longitude is required, and from the of the intervals of time, results a most pared with that observed at, or calculated for, ta for ascertaining differences of longitude; but by on, we obviate any error in the position of the in |