These are a few of the many contradictory opinions of philosophers concerning the earth, and we find that the learned have had equal perplexity as to the nature of the sun. Some of the ancient philosophers have affirmed that it is a vast wheel of brilliant fire;[5] others that it is merely a mirror or sphere of transparent crystal;[6] and a third class, at the head of whom stands Anaxagoras, maintained that it was nothing but a huge ignited mass of iron or stone--indeed he declared the heavens to be merely a vault of stone--and that the stars were stones whirled upward from the earth, and set on fire by the velocity of its revolutions.[7] But I give little attention to the doctrines of this philosopher, the people of Athens having fully refuted them by banishing him from their city; a concise mode of answering unwelcome doctrines, much resorted to in former days. Another sect of philosophers do declare, that certain fiery particles exhale constantly from the earth, which, concentrating in a single point of the firmament by day, constitute the sun, but being scattered and rambling about in the dark at night, collect in various points, and form stars. These are regularly burnt out and extinguished, not unlike to the lamps in our streets, and require a fresh supply of exhalations for the next occasion.[8] It is even recorded that at certain remote and obscure periods, in consequence of a great scarcity of fuel, the sun has been completely burnt out, and sometimes not rekindled for a month at a time. A most melancholy circumstance, the very idea of which gave vast concern to Heraclitus, that worthy weeping philosopher of antiquity. In addition to these various speculations, it was the opinion of Herschel that the sun is a magnificent, habitable abode; the light it furnishes arising from certain empyreal, luminous or phosphoric clouds, swimming in its transparent atmosphere.[9] But we will not enter further at present into the nature of the sun, that being an inquiry not immediately necessary to the development of this history; neither will we embroil ourselves in any more of the endless disputes of philosophers touching the form of this globe, but content ourselves with the theory advanced in the beginning of this chapter, and will proceed to illustrate by experiment the complexity of motion therein described to this our rotatory planet.