These satellites are quite small--they are the smallest celestial bodies we know. The brightness of the planet prevents us from measuring them exactly. It seems, however, that the nearer is the larger, and shows the brightness of a star of the tenth magnitude, and that the second shines as a star of the twelfth magnitude. According to the most trustworthy photometric measures, the first satellite may have a diameter of 7.45 miles, and the second a diameter of 6.2 miles. _The larger of these two worlds is scarcely larger than Paris._ Should we honor them with the title of worlds? They are not even terrestrial continents, nor empires, nor kingdoms, nor provinces, nor departments. Alexander, Cæsar, Charlemagne, or Napoleon, might care but little to receive the scepter of such worlds. Gulliver might juggle with them. Who knows, however? The vanity of men being generally in the direct ratio of their mediocrity, the microscopical reasoning mites which doubtless swarm on their surface have also, perhaps, permanent armies, which mutilate each other for the possession of a grain of sand. These two little moons received from their discoverer the names of _Deimos_ (Terror) and _Phobos_ (Flight), suggested by the two verses of Homer’s “Iliad” which represent Mars descending on the earth to avenge the death of his son Ascalaphus: “He ordered Terror and Flight to yoke his steeds, And he himself put on his glittering arms.” _Phobos_ is the name of the nearer satellite; _Deimos_, that of the more distant. The existence of these little globes had already been suspected from analogy, and thinkers had frequently suggested that, since the earth has one satellite, Mars should have two, Jupiter four, Saturn eight; and this is indeed the fact--though as Jupiter is now found to have _five_ satellites, this arithmetical progression is upset. But as we experience too often in practice the insufficiency of these reasonings of purely human logic, we can not give them more value than they really possess. We might suppose in the same way now that Uranus has sixteen satellites, and Neptune thirty-two. This is possible; but we know nothing of them, and have not even the right to consider this proportion as probable. It is not the less curious to read the following passage, written by Voltaire in 1750 in his masterpiece, the “Micromégas:” “On leaving Jupiter, our travelers crossed a space of about a hundred millions of leagues, and reached the planet Mars. They saw _two moons_, which wait on this planet, and which have escaped the gaze of astronomers. I know well that Father Castel wrote against the existence of these two moons; but I agree with those who reason from analogy. These good philosophers know how difficult it would be for Mars, which is so far from the sun, to get on with less than two moons. However this may be, our people found it so small that they feared they might not find anything to lie upon, and went on their way.”