URANUS and NEPTUNE are much smaller bodies than Jupiter and Saturn, though far larger than the Earth. But their distance from the Earth and Sun makes their discs small and faint, and they show little in the telescope beyond a hint of "belts" like those of Jupiter; so that, as with that planet, the surfaces that they show are almost certainly the upper surfaces of a shell of cloud. In general, therefore, the rule appears to hold good throughout the solar system that a very large body is intensely hot and in a condition of violent activity and rapid change; that smaller bodies are less hot and less active, until we come down to the smallest, which are cold, inert, and dead. Our own Earth, midway in the series, is itself cold, but is placed at such a distance from the Sun as to receive from it a sufficient but not excessive supply of light and heat, and the changes of the Earth are such as not to prohibit but to nourish and support the growth and development of the various forms of life. The smallest members of the solar system are known as METEORS. These are often no more than pebbles or particles of dust, moving together in associated orbits round the Sun. They are too small and too scattered to be seen in open space, and become visible to us only {80} when their orbits intersect that of the earth, and the earth actually encounters them. They then rush into our atmosphere at a great speed, and become highly heated and luminous as they compress the air before them; so highly heated that most are vapourised and dissipated, but a few reach the ground. As they are actually moving in parallel paths at the time of one of these encounters, they appear from the effect of perspective to diverge from a point, hence called the "+radiant+." Some showers occur on the same date of every year; thus a radiant in the constellation Lyra is active about April 21, giving us meteors, known as the "Lyrids"; and another in Perseus in August, gives us the "Perseids." Other radiants are active at intervals of several years; the most famous of all meteoric showers, that of the "Leonids," from a radiant in Leo, was active for many centuries every thirty-third year; and another falling in the same month, November, came from a radiant in Andromeda every thirteen years. In these four cases and in some others the meteors have been found to be travelling along the same path as a comet. It is therefore considered that meteoric swarms are due to the gradual break up of comets; indeed the comet of the Andromeda shower, known from one of its observers as "Biela's," was actually seen to divide into two in December 1845, and has not been observed as a comet since 1852, though the showers connected with it, giving us the meteors known as the "Andromedes," have continued to be frequent and rich. Meteors, therefore, are the smallest, most insignificant, of all the celestial bodies; and the shining out of a meteor is the last stage of