'Off on a Comet ' Summary

They first notice weight loss: Captain Servadac's adjutant Ben Zoof, to his amazement, jumps 12 m (39 ft) high. Zoof with Servadac also soon notice that the alternation of day and night is shortened to six hours, that east and west have changed sides, and that water begins to boil at 66 °C (151 °F), from which they rightly deduce that the atmosphere became thinner and pressure dropped. At the beginning of their stay in Gallia they notice the Earth with the Moon, but think it is an unknown planet. Other important information is obtained through their research expedition with a ship, which the comet also took.

During the voyage they discover a mountain chain blocking the sea, which they initially consider to be the Mediterranean Sea and then they find the island of Formentera (before the catastrophe a part of the Balearic Islands), where they find French astronomer Palmyrin Rosette, who helps them to solve all the mysterious phenomena. They are all on a comet which Rosette discovered by a year ago and predicted to be on a collision course with Earth, but no one believed the astronomer, because a layer of thick fog at the time prevented astronomical observations in other places.

A new research expedition determines the circumference of Gallia to be 2,320 km (1,440 mi). The mass of the comet is calculated by Rosette. He determines it at 209,346 billion tonnes. For the calculation he uses spring scales and forty 5-franc silver coins, the weight of which on earth equaled exactly 1 kg (2.2 lb). However, the owner of the scales, Isaac Hakkabut, has rigged the instrument, so the results have to be cut by a quarter.