50 LATITUDE AND LONGITUDE. 



but it is possible that one person with a good sextant 

 may perform the whole. Thus: Let the obser- 

 vations be taken in the following order, noting the 

 times by a watch : 



1 . The altitude of the Star or Sun ; 



2. The altitude of the Moon ; 



3. Any number of distances ; 



4. The altitude of the Moon again ; 



5. The altitude of the Sun or Star again. 



Add together the distances and the times when 

 taken, each of which, divided by the observed number, 

 gives the mean time and distance. 



To reduce the altitudes to the mean time, we make 

 this proportion ; as the difference of times between 

 the observations is to the difference of their altitudes, 

 so is the difference between the time that the first alti- 

 tude was taken and the mean time to a fourth term ; this 

 added to or subtracted from the first altitude, according 

 as it is increasing or decreasing, gives the altitude re- 

 duced to mean time. 



The Stars commonly employed for lunar observations 

 and used in the Nautical Almanac are <i Arietis, Al- 

 debaran, Pollux, Regulus, Spica Virginis, Antares, 

 a Aquila, Fomalhaut and -: IVgasi. 



For a variety of necessary corrections and circum- 

 stances connected with lunar observations in a practical 

 sense, see " Noire 's Navigation," Page 210. 



OF LATITUDE. By the figure just before alluded to 

 we are enabled to comprehend that the latitude of any 

 place is its distance from the Equator, and since all the 

 points of a parallel passing through any given place 

 are equally distant from the Equator, therefore all 

 places situated on this same parallel have the same 

 latitude. 



Since the longitudinal distance is measured on any arc 

 of the Equator E M, intercepted between any two given 

 meridians NES, NMS, so the latitude is counted in 

 degrees, &c., on some arc of the Meridian MO, orMP, 

 intercepted between any given Parallel APB, COG 

 and the Equator EMQ ; which, it is clear, is either 



