NavList:

   

Reply

I agree with Wolfgang's comparison and assessment. Here is an extract taken 
from "snippet" views in Google Books:

"  The great Dutch physicist, Huygens, tried to make an ingenious pendulum 
clock which would be able to go at sea, but the attempt failed. Others, 
however, went on trying, and in the end they succeeded.
   In the year 1713 several British shipowners demanded that the Government 
offer a prize for the person who discovered a good method of determining 
longitude at sea. That was done the following year. The reward offered was 
?20000 and it was to be distributed by a Board of Longitude. The stipulation 
was that the error after six weeks' sailing should not exceed 30 geographic 
miles, that is to say an average error of less than three seconds (of time) a 
day. There was no pendulum clock on land capable of that. Sir Isaac Newton 
enumerated the various methods for the Board and also told them that it was 
theoretically possible to keep time exactly with a clock; but by reason of a 
ship's motion, changes from heat to cold, damp to dry, and differences in 
gravity at different latitudes, the clock which could do so had not yet been 
made. 

[...]

   Headed by the Astronomer Royal, Maskelyne, they devoted all their interest 
to perfecting the method using lunar distances. Huygens had failed with his 
clock, contemporary horology had nothing to give the navigator. 
   However, in the year 1728 there came to London a young clockmaker who had 
originally been a cabinet-maker. He determined to try to win the huge 
longitude prize. It was a daring decision, for it called for a revolution in 
the art of making clocks. English instrument-making was then at a very high 
level and John Harrison obviously felt that the possibility existed.
   The Board of Longitude would have nothing to do with the mad Yorkshire 
cabinet-maker, but all the same after six years he had his first model ready. 
It was a complicated, well-executed machine, a small pendulum clock with two 
pendulums, joined by a spring which was to equalize the shocks of the ship's 
motion. Despite considerable opposition from the moon-worshippers on the 
Board, the Admiralty agreed that Harrison should be allowed to test his 
timepiece in a naval vessel, HMS Centurion. The chronometer fulfilled the 
Board's requirements, but Harrison was not given the prize. The Board had not 
yet despaired of its lunar distances. Harrison, however, was of tough 
Yorkshire stock and he did not give up either. He made model after model, 
each better than the previous one, and finally so small that you could carry 
them in a coat pocket. They are still going in the museum at Greenwich. 
   Harrison's chronometers made repeated voyages across the ocean ; they kept 
time in storms and showed the correct time in the heat of the tropics, nor 
did the diminished gravity of the equatorial regions affect them in any way, 
for they had no pendulum or weights, but instead an oscillating wheel, a 
balance-wheel, driven by a spring. The Board of Longitude, headed by 
Maskelyne, still fought tooth and nail, but when Harrison at the age of 83 
completed his fifth chronometer model,  the King gave orders that he should 
be given the prize and so he got his ?20000. Navigators had thus acquired a 
means of determining longitude, for with one of Harrison's chronometers they 
always had reliable Greenwich time on board. None the less, the 
lunar-distance method long continued to be used at sea, and it was still 
taught in navigation classes for several generations. The fault in it, 
perhaps, is that sailors do not as a rule have time to be astronomers, and 
astronomers as a rule understand too little of navigation. "

So basically the standard popular re-telling though briefer than most. For a 
sense of scale, the above text is from pp.139-140 out of 195.

-FER




--~--~---------~--~----~------------~-------~--~----~
NavList message boards: www.fer3.com/arc
Or post by email to: NavList@fer3.com
To , email NavList-@fer3.com
-~----------~----~----~----~------~----~------~--~---

   

Reply