of Nautical Astronomy. 325 
could not be computed to within less than 10 or 12 minutes of 
the truth ;—an error which would sometimes have rendered the 
longitude “deduced froma lunar distance, uncertain to the extent 
of eight degrees. Therefore, though this method of finding the 
jongitude at sea appeared the most eligible of any that presented 
itself, it was at that time abandoned as altogether impracticable. 
When Dr. Maskelyne succeeded to the situation in 1765, such 
advances had been made in astronomical science, that under his 
auspices this method of finding the lougitude (which in the in- 
terval had never been lost sight of) was again brought forward ; 
and after devoting a great portion of his long and valuable life 
to bring the method to perfection, he had the satisfaction of 
seeing his meritorious exertions crowned with almost complete 
success, 
One of the great obstacles to its introduction into general 
practice, was the difficulty in making the necessary calculations 
from the tables and formulas which the labours of astronomers 
had supplied. But this formidable objection was completely 
obviated by the publication of the Nautical Almanac, which on 
Dr. Maskelyne’s suggestion was undertaken by the Board of 
Longitude in 1766, and it has ever since been continued an- 
nually. 
Before mariners in general, however, could be materially bene- 
fited by all these efforts for their advantage, it was requisite that 
they should be furnished with such instruments for observing, as 
they could use with readiness, and depend upon with confidence ; 
and with simple as well as appropriate rules for making the ne- 
cessary calculations after their observations were completed. 
The artists of this country answered well to the call which 
this consideration made upon their talents, and devised such im- 
provements in the construction and graduation of quadrants, 
sextants and circles, for nautical observations, that nothing ap- 
pears left to be desired on the subject. And in all the useful 
problems in the practice of nautical astronomy, the methods of 
performing the calculations have been so simplified, that it is 
not easy to conceive for what situation connected with the na- 
vigation of a ship, the person is fitted who is incapable of com- 
prehending them. 
It haz been fortunate for Astronomy, that theory aud observa- 
tion have advanced simultaneously. From successive improve- 
ments in the instruments and the art of observation, the abstruse 
deductious of theory have been regularly subjected to the sound 
practical test of comparison with observed phenomena; while 
the apparently anomalous facts of observation have pointed to 
important consequences of the theory, which might otherwise for 
a time have been either neglected or overlooked. Under these 
salutary checks, the progress of the science has been distinguished 
by 
