which take from the Tables, and subtract from 90°; the result is the latitude required.

EXAMPLE.

Oct. 11, 1845, in latitude by account 54° N. and long. 83° 15′ W., the following double altitude of the sun was observed.

The run of the ship in the interval was S. by W. 15 miles, index correction + 5' 10" and the height of eye above the sea was 18 feet: required the true latitude at the second observation.

(143) June 3, 1847, in latitude by account 52° N., and long. 72° E., the following double altitude of the sun

The run of the ship in the interval was W. by S. 10 miles, index correction - 0' 40" and height of eye 12 feet, required the true latitude at the second observation.

Ans., 50° 48' N.

(144) April 11, 1847, in latitude by account 50° 20′ N. long. 10° 30′ E., the following double altitude of the sun was observed.

The run of the ship in the interval was N.N.E. 29 miles, index correction + 2' 10" and height of eye 18 feet; required the true latitude at the second observation.

Ans., 56° 56′ N.

(145) April 13, 1847, in latitude by account 41° 20' N.,

long. 156° 15' E., the following double altitude of the sun

The run of the ship in the interval was S.S.E. 25 miles, index correction was 5' 20" and height of eye 14 feet, required the true latitude at second observation.

Ans., 41° 23' N. (146) April 22, 1847, in latitude by account 50° 48' N., and long. 148° 30′ E., the following double altitude of the

The run of the ship in the interval was O, index correction +40" and height of eye 0, required the true latitude at second observation. Ans., 50° 41' N.

(147.) Oct. 15, 1848, in latitude by account 53° N., and long. 54° E., the following double altitude of the sun was observed.

The run of the ship in the interval was S. by W. 14 miles, index correction + 2′ 55′′ and height of eye above the sea 15 feet, required the true latitude at second observation. Ans., 53° 17' N.

(148.) Oct. 24, 1849, in latitude by account 50° 40′ S., and long. 142° W., the following double altitude of the sun

The run of the ship in the interval was 0, and height of

eye above the sea 0, required the true latitude at second Ans., 50° 45′ S.

observation.

Second. When the objects observed are two stars taken at the same instant.

Rule XXXVII.

1. Correct the observed altitudes for index correction, dip, and refraction, and thus find the true altitudes, which subtract from 90° for the true zenith distances.

2. Take out of the Nautical Almanac the right ascension and declination of the two stars, and get their polar distances as in (3) p. 144.

3. To find the polar angle. The difference between the right ascensions of the two stars is the polar angle.

ence.

4. To find are 1 (using Inman's Tables). Put down the two polar distances under each other, and take their differAdd together the log. sin of the polar distance at greater bearing, the log. sin. of polar distance at less bearing, and the log. haversine of polar angle; the result, rejecting 10 in the index, is the log. haversine of an arc, which take from the tables and call arc A.

Add together versine of arc A and versine of the difference of polar distances; the sum will be the versine of arc 1, which find in the tables. Then proceed to find arc 2, &c., as in Rule 36, p. 145.

EXAMPLE.

January 1, 1846, in latitude by account 38° 10′ N.,