The case of Uranus introduces us to another class of conditions fatal to habitability. The equator of Jupiter is inclined only 3° to the plane of its orbit; the difference in its seasons is, therefore, almost imperceptible; there is hardly any alteration in the incidence of the solar rays; it is, as if on the Earth, the height of the Sun at noon in mid-winter were what it actually is on the 14th of March, and its height at midsummer the same as we observe on March 28. The inclination of the equator of Saturn is considerably greater than that of Mars or the Earth, so that its seasons are more pronounced, but not to an extent that would introduce any radical difference. But for Uranus, the inclination of the equator to the plane of the orbit is 82°. If this were the case for the Earth, the noonday sun for London would be, at the spring equinox, 38-1/2° high as at present, but its altitude day by day would increase with great rapidity, and before the end of April, the Sun at noon would be right in the zenith, and 13° above the horizon at midnight. At midsummer, indeed, it would be only 59° high at noonday, but it would be north of the zenith instead of south, and at technical midnight, it would still be 44° in altitude, thus moving round in a very small circle, only 15° in diameter. From about April 18 to August 25--that is to say, for 129 days--the Sun would never set, and unlike the summer day of our own polar regions now, wherein the Sun, though always present, is always low down in the sky, for much of that period it would pass the meridian quite close to the zenith. As the year of Uranus is 84 times the length of our year, the London of Uranus would have to endure not far short of 30 years continuous scorching. And the winter would be as long; the perpetual day of summer would be replaced by a night as enduring. More than 29 years of unbroken darkness, of unmitigated cold, cannot possibly ever consist with the conditions necessary for life upon a planet. Whatever the brightness of the imagined sun of Uranus, if for 29 years at a time that sun were below the horizon, the water on the planet must be congealed, and during the 29 years of unbroken day all the water would be as certainly evaporated. Thus, though Uranus is not burdened by the enormous mass of Jupiter, nor overshadowed, like Saturn, by a system of rings, the extraordinary inclination of its axis introduces a condition which is as fatal to it, as a world to dwell in, as any of the disabilities of the other planets.