87. Q. What is their velocity? A. Their average velocity is thirty-five miles a second, and it sometimes rises to one hundred miles a second.
88. Q. What does Prof. Peirce state as the result of his investigation in regard to meteors? A. That the heat which the earth receives directly from meteors is the same in amount which it receives from the sun by radiation, and that the sun receives five-sixths of its heat from the meteors that fall upon it.
89. Q. When the bodies are large enough to bear the heat, and the unconsumed center comes to the earth, what are they called? A. Aerolites or air-stones.
90. Q. What is said of the distribution of these bodies through space? A. They are not evenly distributed through space. In some places they are gathered into systems which circle round the sun in orbits as certain as those of the planets.
91. Q. How many such systems of meteoric bodies has it been demonstrated that the earth encounters in a single year? A. More than one hundred.
92. Q. What are comets? A. They are clouds of gas or meteoric matter, or both, darting into the solar system from every side, at every plane of the ecliptic, becoming luminous with reflected light, passing the sun, and returning again to outer darkness.
93. Q. What appendage do comets usually have? A. A tail, which follows the comet to perihelion, and precedes it afterwards.
94. Q. What is the character of the orbits of some comets? A. Very enormously elongated. One end may lie inside the earth’s orbit, and the other end be as far beyond Neptune as that is from the sun.
95. Q. How many comets have been visible to the naked eye since the Christian era? A. Five hundred.
96. Q. How many have been seen by telescopes since their invention? A. Two hundred.