1110 



NAVIGATION-NAUTICAL ASTRONOMY. [rAMPira IN UHtorruDi. 



Moon's altitude. 



Ob., alt L. L. . . . 22 68* 42" 

 Dip . 4' 4V ) 



Semi. . + 15' 11' | 

 Aug. + 5' -5 ) 



App. alt . . 

 Par. and rvf. 



True alt 



10' 



23 3' 4'(oO 

 + 48' 38' 



23 61' 42" (A') 

 90 



Co-altitude .... 06 8'18"-ZM 



Fur the Time at Greenwich. 

 ( >!.*.. l..,t. 06 25' 31* 



Moon's semi. . 

 Sun's seiui 



15 11 

 15 49 



= 6J 50 31 



d, 66 56' 31* 



o, 58 4 35 comp. cos. -2707183 



a, 23 3 4 comp. cos. -0361386 



2)138 4 10 



| gum, 69 2 5 



i sum <s.d,\-2 5 34 



- A, 68 3 59 



A', 23 51 42 



A + A', 81 55 41 



cos. 9-5336429 

 cos. 9-9902543 



cos. 9 7234034 

 cos. 9 -9611955 



2)39-5413530 



19-7706766 

 1 (A + A 1 ), 40 67 50J - cos. 9 -8780168+ . 



0, 61 21 13 



0, 

 D = 28 8 13J 



, 9-8920507 





two to be 



luliled 



cos. 9-7955409+ ' to S ether - 

 sin. 9-6735577 = their sum. 



.'. D 56 16 27 the true distance. 

 Dis.at21h.65 15 36 Prop. log. ditf. -3221 - 



Difference 1 51 



Mean time after 21h. 



at Greenwich . 



.'. Greenwich mean 



time . . . 



. -4710 



2h. 7m. 453. '1489 

 23h. 7m. 45s. 



Having thus determined the time at Greenwich when 

 the lunar distance was taken, we can compute the right 

 Moension and declination of the moon to greater pre- 

 cision than the time by account could be expected to 

 give. It so happens that, in thin particular example, the 

 time, by account, is very nearly the same aa that deduced 

 fn>m the observations ; but yet there would be a sen- 

 sible difference in the resulting longitude, if the com- 

 putation of the ship time had preceded that for the 

 .Meh time. 



It is only in reference to the moon that much accuracy 

 in the time and longitude, by account, is of any 



For the Mean Time at the Ship. 



Son's R A. 

 21rt , . 3h. 66m. 53 8s. 

 ISlh. . . + 3m. 46s. 

 7u. 45s. . 1 3s. 



Moon's R. A. 

 23h. . . 7n. 65m. 24s. 

 7m. 45s. . + 16s. 



R. A.= 7h. 55in. 40s. 



II. A. - 4h. Om. 41s. 



Moon's declination. 

 23h. 17' 5' 12" N. 



7ui. 45s. . . 1 2 



Deo. - 17 4 1< N. 



The data for computing the moon's hour-angle with the 

 UK ridian are therefore as follows : namely 



ZM - 66 8' 18', PZ - 39 \V, PM - 72 66' 50* 



/ M. i;ii" 8' 18' 

 PZ, 39 12 comp. sin. -10 

 PM, 72 66 60 cornp. sin. O1'.'.V, '<> 



2)178 16 8 



,89 84.. sin. 9-9999503 

 s-Z M, 22 59 46 . . sin. 9-6918086 



2)19-8105867 



\ P, 36 28 46 . . cos. 9-9052933 



.*. P, 72 57 32 the moon's hour-angle 

 2 



3)14,6 6,5' ,4' 



4h. 50m. 

 1m. 60s. 



Moorf. hour-angle in 



Moon's R.A. 7h. 55m. 40s. 



R A. of meridian 3h. 3m. 60s. 

 Suu'sR.A. 4k Om. 41s. 



Sun's hour-angle with ) n , Kf , K , ( before noon of 

 meridian . Oh ' 5Cm - 51s ' the 22ud. 



24h. 



Mean time at ship 23h. 3m . 9s. May 21st. 

 Moan time at Greenwich 23h. 7m. 45s. 



Longitude W. in time Oh. 4m. 36s. .' . Long. W. 1 9'. 



Although the Greenwich time, by account, differs by 

 only a few minutes from the Greenwich time as deter- 

 mined by the observation, yet the longitude would have 

 differed by more than 4' from the result here arrived at, 

 if the ship time had been determined before the Green- 

 wich time. It thus appears, that it is in all cases more 

 prudent to compute the time at Greenwich before that 

 at the ship, when the latter is to be deduced from the 

 moon. 



Examples for Exercise, 



\. On March 25, 1847, at 3h. 30m. P.M., mean time 

 nearly, in latitude .".-_' N., and longitude by account 33 

 W., the following lunar observation was takeu : 



Obs. alt. sun's L.L. Obs. alt. moon's L.L. 



23 Iff 20' 23 60' 10" 



Index cor. - 6 10 Index cor. +6 



Obs. dist. nearest limbs. 



112 56' 30* 

 Index cor. 4 20 



The height of the eye was 20 feet, and the following par- 

 ticulars were furnished by HieNauticul Almanac: namely, 



Sun's dec. Equa. of time. 



Mar. 25, 1 40* 56' N. 6tn. 13 -8s. additive. 



26, 2 4' 29' N. 6m. 55 '2s. 

 Moon's semi. Hor. par. Sun's semi, 



noon 25th, 14' 59' noon 54' 59' 16' 3' 

 midnight 14' 55* mid. 64' 44" 



Also distance at 3h., 111 33' 34"; at 6h., 112 57' 1C'. 

 Required the. longitude of the ship. Ans. 32 iV.iJ' \V. 

 2. On January 9, 1851, at 7h. 50m. r.M., mean time 

 in ;irly, in latitude 49 40* N., and longitude by account 

 10 li., the following lunar observation was taken : 



