The Ballad of John Harrison

O who can solve this problem?
Sighed the Lords of Admiralty
How can we know our longitude
When far away at sea?
 
So many ships have foundered
So many sailors lost
So many cargoes brought to us
At such a dreadful cost.
 
A reckoning of latitude
Can easily be made,
But working out the longitude

Is a tricky task indeed.

(first three verses only...)