Dr. Maskelyne’s formulae for finding the longitude, &c. 141 
Rules for ascertaining the longitude from the preceding formulce. 
1. The longitude falls in the first, second, third, or fourth 
quadrant, according as the right ascension is in the first, 
second, third, or fourth quadrant, unless the auxiliary angle 
B be equal to or greater than qo°. 
2. If B be equal to go° the longitude = 0, if the right as- 
cension is in the first or fourth quadrant ; but if the right 
ascension is in the second or third, the longitude = 180°. 
3. If B be greater than 90° the following are the conse- 
quences. If the right ascension is in the first quadrant, the 
longitude falls in the fourth, and on the contrary, if the right 
ascension is in the fourth, the longitude falls in the first. If 
the right ascension is in the second, the longitude falls in the 
t lhir d, and on the contrary, if the right ascension is in the third, 
the longitude falls in the second. 
4. If S be on the equinoctial colure, as represented in Fig. 
3 and 6 , (PI. VI.) the following are the consequences. If S be 
between the first point of aries and P the longitude falls in the 
first quadrant, but if S be between the first point of libra and 
P the longitude falls in the second. If S be between the first 
point of aries and p the longitude falls in the fourth quadrant, 
but if S be between the first point of libra and p the longi- 
tude falls in the third quadrant.* 
The first of these rules will be evident after the second 
and third are demonstrated. 
* No provision is made in Dr. Masjcelyne’s formula; for ascertaining the longi- 
tude of a celestial object on P p in either of the two hemispheres. 
