EXPLANATION OF THE TABLES. 221 
and the length of the day and night in lat. 46 ° n., and the declination 
1 8 ° N. 
Tabular value answering to lat. 46 ° and decl. 18 0 is 7 h. 19 m. Hence 
in lat. 46 ° n., decl. 18 0 n., time of sunset is 7 h. 19 m., and that of sunrise 
12 h. — 7 h. 19 m. = 4 h. 41 m. 
The same is true for lat. 46 ° s., decl. 18 0 s. 
Conversely, both for lat. 46 ° n., decl. 18 0 s., and for lat. 46 ° s., decl. 
18 ° N., the time of sunrise is 7 h. 19 m., and that of sunset is 4 h. 41 m. 
In the first pair of cases the length of the day is 7 h. 19 m. x 2 = 
14 h. 38 m., and that of the night is 4 h. 41 m. x 2 = 9 h. 22 m.; and in 
the second pair, conversely, the length of the night is 14 h. 38 m., and that 
of the day 9 h. 22 m. 
Example .—At what time (apparent) does the star a OphiucJii rise and 
set on May 12 th, in lat. 30 s. ? 
ir. m. 
Star’s B. A. 1729 
Suns B. A. .. .. 3 15 
Star’s approximate meridian passage. 1414 
Time answering in taUe to 30 ° s. lat., and star’s] 
declination 12 0 39 ' n. = 6 h. 30 m. which, sub-> 5 30 
tracted from 12 , gives 5 h. 30 m. J 
Bemainder = time of star’s rising . 8 44 
Sam = time of star’s setting .. 19 44 p m. 
or . 7 44 A.M. 
Table IX., giving the distance of the horizon as seen over water from 
different heights above it, will be found very useful both in checking 
exaggerated estimates of the width of lakes whose opposite shores are 
invisible, and also as a rude means of judging the distance of objects seen 
across water. 
Table X. gives the values of 2 - S ^alMiuur angle and uscd . Q 
sm 1" 
finding the latitude by altitudes of the sun, or of stars when they are near 
the meridian. 
