Local time is the time related to the meridian of the place of observation, the same for all places of the same geographical longitude. “True local time,” as shown for instance by a sundial, is dictated daily by the culmination of the sun, and fluctuates with the rhythm of the equation of time. “Mean solar time,” that is, the solar time calculated in reference to the ecliptic and the elliptical shape of the Earth's orbit, as yet had no practical role, but the social acceleration in communication around the year 1800 meant that the dependency of local time on geographical lon…