[Footnote 15: We should next see the Pacific Ocean.] It is amusing enough, said the Marchioness, to fancy oneself in a situation to see all these things: but if I were taking the view I should wish for the power of hastening or retarding the earth's motion, according to the feelings with which each object inspired me: I assure you I should soon push on those that argued on politics, and the others that devoured their enemies; but there are some of the people you have been speaking of that would excite my curiosity; the handsome Circassians, for instance, whose customs are so peculiar. But a serious difficulty occurs to me respecting your system. If the earth turns, we every moment change our atmosphere, and respire that of a new climate. By no means, madam, I replied; the air which surrounds the earth rises only to a certain height, twenty leagues perhaps at farthest;[16] this atmosphere always turns with us. You have doubtless observed the sort of shell in which a silk-worm imprisons itself, and which it forms with such astonishing art. It is composed of silk closely woven, but covered with a light down. Thus it is with regard to the earth, it is a solid body covered with an atmosphere extending to a certain height, which adheres to, and moves with it, as the down does with the firmer substance beneath it. Above our atmosphere is the celestial matter, incomparably more pure, subtile and active than air. [Footnote 16: Even at two leagues it is no longer discernible.] You represent the earth in a very contemptible light, said the Marchioness. Nevertheless on this silk-worm's shell we find stupendous works, furious wars, and universal agitation. Yes, answered I, and while all this is going on, nature, who does not concern herself about such frivolous things, carries us all along, with an uninterrupted motion, and amuses herself with the little ball. It appears very ridiculous, replied she, to give way to so much anxiety, whilst one is living on a thing that is perpetually turning; but unfortunately we are not assured that it does turn, for, to tell you the truth, all the precautions you take to convince me that we should not feel its motion are unsatisfactory. How could it avoid giving some indication by which we should be sensible of it?[17] The most common and natural motions, said I, are the least felt: this observation is true even in a moral sense: the motions of self-love are so frequent in our minds, that for the most part we are not sensible of them, but believe ourselves actuated by other principles. Ah! you are beginning to moralize, said she; moralizing and explaining natural philosophy are a little different; I fancy you grow tired of your subject: let us return home, we have had enough for the first lecture. To-morrow we will come here again--you with your systems, and I with my ignorance. [Footnote 17: There are several; one of them is the aberration of the stars. Astron. Book xvii.]