Galilean moons century when other inner moons were discovered, and Marius' names became widely used. Galileo was able to develop a method of determining longitude based on the timing of the orbits of the Galilean moons. The times of the eclipses of the moons could be precisely calculated in advance, and compared with local observations on land or on ship to determine the local time and hence longitude. The main problem with the technique was that it was difficult to observe the Galilean moons through a telescope on a moving ship; a problem that Galileo tried to solve with the invention of
Galilean electromagnetism to any consistent Galilean limit. Rousseaux gives a simple example showing that a transformation from an initial inertial frame to a second frame with a speed of v with respect to the first frame and then to a third frame moving with a speed v with respect to the second frame would give a result different from going directly from the first frame to the third frame using a relative speed of (v + v). Le Bellac and Levy-Leblond offer two transformations that do have consistent Galilean limits as follows: The electric limit applies when electric field effects are dominant