navigation. 
many miles arc contained in a degree in la- 
titude 18 ; I find there are 57.06. There- 
fore it must be evident, that, as the latitude 
recedes from the equator, the smaller the 
degrees of longitude become: hence, if a 
vessel could sail round the north pole in la- 
titude 80", where there are only 10" 42' 
miles in a degree of latitude, and were to 
run 123 miles in the twenty-four hours, she 
would sail ten times round the pole, and in- 
deed round the world, in that time, and see 
the sun rise and set no less than twelve 
times ! 
From this we are satisfied that the old 
practice of laying down a chart, or map, in 
square degrees was erroneous in the ex- 
treme ; and that wliat is called “ Merca- 
tor’s projection,” which gives every degree 
its just and exaet value in breadth, at both 
its northern and its soutliern extremities, is 
the only correct and rational mode of des- 
cription. 
We shall now give the reader a few ex- 
amples under the head of plane sailing, 
which supposes the earth to be a perfect 
level, or plane. This is but the application 
of plane trigonometry to tire solution of the 
several variations; where the hypothenuse, 
or longest side, is always the rhumb on 
which the ship’s course lies. The perpen- 
dicular is the difference of latitude counted 
on the meridian, and the base the depar- 
ture (which is either easting or westing) 
counted from the meridian. The angle op- 
posite the base is that which the ship makes 
with the meridian : the angle at the per-_ 
pendicular is the complement of the course ; 
which, taken together, always make 90 
degrees, or eight points. When the course 
is given in degrees, they must be set off 
from a line of chords of 00, corresponding 
with the radius of tlie circle, or quadrant, 
drawn either easterly or westerly, as the 
ship’s course may be, from the meridian. 
Wliere the course is given in "points, it may 
be set down with its corresponding loga- 
rithm in points in the calculation, as found 
in the first page of logarithms in general. 
In all cases, wherever the complement 
course is used, the degrees, or points, put 
down, correspond with the course itself; yet 
the logarithm belonging to the complement 
of that course is taken. 
Example 1. “ Course and distance sailed 
being given, to find the difference of lati- 
tude, and the departure from the meridian.’’ 
Suppose a ship from the Lizard, in the lati- 
tude of 49“ .57' nortli, sails S. W. by W. 496 
miles ; required the latitude come to, and 
her departure from the meridian. Draw 
the meridian, or difference of latitude; with 
the chord of 60“ in your compasses, and one 
foot in C, (fig. 14) describe an arch : take 
56“ 15', or five points, in your compasses, 
and lay off that distance upon the arch, from 
B C towards C A; through the point where 
it cuts draw the distance C A, upon which 
set off' 496 : from A let fall the perpendicu- 
lar A B, the departure, and it is done. For 
A B, being measured on the same scale that 
A C was, will give the departure 412.4, and 
B C 275.6, for the difference of latitude. 
Example 2. “ Course and difference of 
latitude being given to find the distance 
. run, and the departure from the meridian.” 
If a ship runs S. E, by E. from 1“ 45' north 
latitude, aqd then by observation is in 
2“ 50' south latitude, required her distance 
and departure ? As the ship has crossed the 
line (i. e. the equator), the north latitude 
1“ 45' must be added to the soutli latitude 
2“ 50' ; which makes the difference of lati- 
tude 4“ 35'. Multiply that by 60, and 
there appear 275 geographical miles. Now 
draw B C (fig. 1.5) equal to 275 ; and B A, 
making an angle with B C equal to five 
points, or 56“ 15': upon C erect the per- 
pendiculars CA, to join B A in A. Then 
will C A be 112, and A B 496 miles ; there- 
fore the ship’s run has been 496 miles, and 
her departure from the meridian 411.6 
easterly. 
Example 3. “ Course and departure being 
given, to find the distance and the difference 
of latitude.” If a ship sails N. E. by E. ^E. 
from a port in 3“ 15' soutli latitude until 
she depart from her first meridian 412 miles, 
what latitude will she be in? Draw DA 
(fig- 16), upon which erect the perpendicular 
A B ; draw the line A C, making an angle 
with A B equal to 64“ 41', corresponding 
with points. At the distance of 412 
miles draw D C, parallel to A B, to cut 
A C in C : through the point C draw B C 
parallel to A D, to cut the meridian A B. 
Thus A C will give 456 miles for the dis- 
tance run, and A B 195 miles for difference 
of latitude. 
Having said thus much by way of general 
information, we must refer those readers 
who are in search of extensive knowledge 
in the art of navigation to the several trea- 
tises which have been written by its profes- 
sors ; among which,we believe, those publish- 
ed by Mr. Nicholson and the late John Ha- 
milton Moore have had the greatest charac- 
ter for utility and general accuracy. With 
respect to what -appertains more to the ex- 
