The Earth's Longitude and the Moon
Despite Harrison's clock, the method of calculating longitude using lunar distances continued well into the nineteenth century. Problems :-
- The clocks were expensive
- Not all ports operated an efficient way of synchronizing these timepieces
Galileo had studied the motions of Jupiter's four moons, the now-named Galilean satellites, and had produced a set of tables with which he hoped to gain some of the prize money then on offer for a reliable way of calculating longitude at sea. In this hoppe, he was unsuccessful, but this method was used widely for mapping land areas. The method was refined by Giovanni Cassini in 1668, who soon afterwards became director of the new Paris Observatory. It was as an offshoot of these developments that Ole Roemer came up with an estimate of the speed of light.
- What difficulties did Galileo's method possess, despite being successfully used for producing maps of land areas ?
- Galileo even went as far as producing and testing a special helmet to be used in his method. What drawbacks would this method have had, over and above the disadvantages mentioned in the previous question ?
- How was Roemer able to use information on the motion of Jupiter's moons to calculate the speed of light ?
- Galileo's researches on pendulum behavior were put to good use in the pendulum clock designed by Huygens. Huygens put this clock forward as a reliable marine timepiece and early trials on sea journeys were successful. Why was this type of clock never developed into a reliable method for ascertaing longitude ?