JOURNAL AND PROCEEDINGS. 93 
moon’s place in the heavens at any future time, toward the latter 
part of the 17th century, the more advanced governments of Europe 
recognized the great value such predictions would be to navigation. 
Increasing commerce with India in the east, and America in the 
west, made some exact method of determining longitude highly 
desirable, especially if it could be made simple enough for general 
use at sea. What was needed, and sought after, was to find the 
exact difference in time between two meridians, as the distance could 
then be readily enough known. The seaman could know from the 
sun’s altitude the time at his meridian of observation, but it was at 
that day impossible for him to know at the moment of such observa- 
tion the exact local time at his first meridian. To meet that difficulty 
two plans were suggested. One was to make accurate timekeepers 
not affected by ordinary changes of temperature, the other was to 
make the moon serve asa chronometer. To accomplish the latter 
task it was necessary to work out in advance at some first meridian 
the exact angular distance, at every hour, between the moon and 
some of the principal stars. By this means, when the seaman had 
taken the exact distance between the moon and a given star, simple 
inspection of his tables would shew him the exact time at his first 
meridian, when moon and star were the same angular distance apart 
as at his observation. 
Charles II. was told in 1674, that such tables of lunar distances, 
worked out in advance, would be of great service to English seamen. 
The result was Greenwich Observatory was founded in 1675, and 
Flamsteed, who furnished his own instruments, was appointed 
“ Astronomical Observator,” at the salary of £100 a year. He de- 
termined with great accuracy the positions of about 3000 stars, and 
made a large number of lunar observations. 
In 1714 the English parliament offered a reward to any discov- 
erer of a method of finding the longitude at sea, the reward to be 
proportionate to the accuracy of the method found out. £410,000 was 
to be given if in a long voyage the method discovered approached 
absolute accuracy within sixty miles, £15,000 if within forty miles, 
and £20,000 if within thirty miles. Many methods were suggested. 
Some of these, as described in a letter by Flamsteed to his assistant, 
Sharp, were most absurd. The problem was at length solved by 
John Harrison, whose improved chronometers brought him, in 
