But what most seriously complicates the Calendar of the Uranians is the fact that the four moons which accompany the planet accomplish their revolution in four different kinds of months, in two, four, eight, and thirteen days, as is shown in the following table:
| Distance from the planet. | Time of revolution. | ||||
| Kilometers. | Miles. | Days. | Hours. | Minutes. | |
| 1. Ariel | 196,000 | 121,520 | 2 | 12 | 29 |
| 2. Umbriel | 276,000 | 171,120 | 4 | 3 | 27 |
| 3. Titania | 450,000 | 279,000 | 8 | 16 | 56 |
| 4. Oberon | 600,000 | 372,000 | 13 | 11 | 7 |
The most curious fact is that these satellites do not rotate like those of the other planets. While the moons of the Earth, Mars, Jupiter, and Saturn accomplish their revolution from east to west, the satellites of Uranus rotate in a plane almost perpendicular to the ecliptic, and it is doubtless the same for the rotation of the planet.
If we had to quit the Earth, and fixate ourselves upon another world, we should prefer Mars to Uranus, where everything must be so different from terrestrial arrangements? But who knows? Perhaps, after all, this planet might afford us some agreeable surprises. Il ne faut jurer de rien.
NEPTUNE
And here we reach the frontier of the Solar System, as actually known to us. In landing on the world of Neptune, which circles through the Heavens in eternal twilight at a distance of more than four milliard kilometers (2,480,000,000 miles) from the common center of attraction of the planetary orbs, we once again admire the prodigies of science.
Uranus was discovered with the telescope, Neptune by calculation. In addition to the solar influence, the worlds exert a mutual attraction upon each other that slightly deranges the harmony ordered by the Sun. The stronger act upon the weaker, and the colossal Jupiter alone causes many of the perturbations in our great solar family. Now during regular observations of the position of Uranus in space, some inexplicable irregularities were soon perceived. The astronomers having full faith in the universality of the law of attraction, could not do otherwise than attribute these irregularities to the influence of some unknown planet situated even farther off. But at what distance?
A very simple proportion, known as Bode's law, has been observed, which indicates approximately the relative distances of the planets from the Sun. It is as follows: Starting from 0, write the number 3, and double successively,
0 3 6 12 24 48 96 192 384.
Then, add the number 4 to each of the preceding figures, which gives the following series: