300 -Mr. Bowditch on the altitude and longitude of the 
These logarithms are calculated for the obliquity 23° 27’ 40"... 
‘The columns marked /at. contain the variations of A, B, C, for an in- 
crease of 100” in the reduced latitude. The column 0d/. contains the 
variations of A, B, C, for an increase of 100” in the obliquity of the 
ecliptic. The signs must be changed, if the latitude or obliquity is 
less than that given in the table. 
Example. 
Required the values of A, B, C, for Salem, when the i is 
23° 27’ 41”°9, 
Tabular numbers 0°079832 9°476637 9°854016 
_ Var. for + 1°+9 obliquity +2 — 14 +4 
Required values _A=0°:079834 B=9°476623 C=9*854020 
The following rule is adapted to the table of log. sines, &c. num- 
bered xxvii in the third edition of the Practical Navigator, in the 
margin of which are placed two columns, one marked P. M. contain- 
ing the double of the time corresponding to the degrees and minutes, 
allowing 15° for an hour; the other marked A. M. containing the 
difference between this and 12hours. Jn using tables not having 
these columns, it will be necessary to turn the time Ty mentioned in the 
rule, into degrees and minutes, and take the log. cotangent of 3 pT instead 
of that mentioned in the rule. . 
RULE. 
Add ta the sun’s right ascension, the apparent time ¢ (count 
ed from noon to noon) and 6 hours, the sum rejecting 24 or 48 hours, 
if greater than those quantities, is to be called the time T; this is to 
be sought for in the column of hours of table xxvii, supposing the : 
column A. M. to be pactedeed 12 hours, as in astronomical compU- 
tation.* The corresponding log. cotangent added to the log. A of 
FP CCER EASES REEDED 
“* Thus if the time T is 5 hours, it must be called 5H.RM. If ists 
