It is certain that mysterious variations actually occur on the surface, notably in the arena of the amphitheatre of Plato as mentioned above. What is also certain is that the lunar globe, 49 times smaller than the earth and 91 times lighter, exerts on its surface a gravitational attraction six times less than that which exists at the surface of our own planet, so that an atmosphere analogous to the air we breathe would be more rarefied and difficult to perceive from here. It is therefore not surprising that this neighbouring world is so different from ours. Besides, seen from a balloon 3 or 4 miles above ground, the Earth appears deserted, uninhabited, as silent as an immense cemetery, and whoever arrived from the Moon in a balloon could ask himself even at that small distance whether there were any people in France or any sound in Paris. Such at least is the impression conveyed to me by my aerial voyages. * * * * * The cold and deathly aspect of our pale satellite was not encouraging for the realisation of the original project of the astronomer J. von Littrow, and soon afterwards, forgetting our nearest neighbour, the imagination of some physicists was bold enough to consider the planet Mars, which is never nearer than 35 million miles, but is the best known of all the countries of the sky and which offers so many points of resemblance with our world that we should hardly feel exiled if we were to transport our household gods thither. The aspect of Mars indeed tends to comfort us after that of the Moon. One could imagine oneself in some terrestrial region. The seasons, summer and winter, autumn and spring, days and night, mornings and evenings, waters, clouds, snows, atmospheric variations, plains adorned with various vegetations--all these things present many resemblances to our own world. The years are longer there since they last 687 days, but the extreme variations of the seasons are about the same as with us since the inclination of the axis is about the same. The days are also a little longer, since the diurnal rotation is 24 hours 37 minutes 23 seconds, but the difference is not great. And you will notice that this is all known with great precision, that diurnal rotation, for example, is known to within one-tenth of a second, or we might even say one-hundredth of a second.