Such is a brief outline of the principal facts known with regard to these interesting but perplexing bodies. We must be content with the recital of what we know, rather than hazard guesses about matters beyond our reach. We see that they are obedient to the great laws of gravitation, and afford a striking illustration of their truth. We have seen how modern science has dissipated the superstition with which, in earlier ages, the advent of a comet was regarded. We no longer regard such a body as a sign of impending calamity; we may rather look upon it as an interesting and a beautiful visitor, which comes to please us and to instruct us, but never to threaten or to destroy. CHAPTER XVII. SHOOTING STARS. Small Bodies of our System--Their Numbers--How they are Observed--The Shooting Star--The Theory of Heat--A Great Shooting Star--The November Meteors--Their Ancient History--The Route followed by the Shoal--Diagram of the Shoal of Meteors--How the Shoal becomes Spread out along its Path--Absorption of Meteors by the Earth--The Discovery of the Relation between Meteors and Comets--The Remarkable Investigations concerning the November Meteors--Two Showers in Successive Years--No Particles have ever been Identified from the Great Shooting Star Showers--Meteoric Stones--Chladni's Researches--Early Cases of Stone-falls--The Meteorite at Ensisheim--Collections of Meteorites--The Rowton Siderite--Relative Frequency of Iron and Stony Meteorites--Fragmentary Character of Meteorites--Tschermak's Hypothesis--Effects of Gravitation on a Missile ejected from a Volcano--Can they have come from the Moon?--The Claims of the Minor Planets to the Parentage of Meteorites--Possible Terrestrial Origin--The Ovifak Iron. In the preceding chapters we have dealt with the gigantic bodies which form the chief objects in what we know as the solar system. We have studied mighty planets measuring thousands of miles in diameter, and we have followed the movements of comets whose dimensions are often to be told by millions of miles. Once, indeed, in a previous chapter we have made a descent to objects much lower in the scale of magnitude, and we have examined that numerous class of small bodies which we call the minor planets. It is now, however, our duty to make a still further, and this time a very long step, downwards in the scale of magnitude. Even the minor planets must be regarded as colossal objects when compared with those little bodies whose presence is revealed to us in an interesting and sometimes in a striking manner.