We will therefore suppose that some of the small vortices, being light and active, slip betwixt the others, and return after they have made their tour, whilst the larger systems remain immoveable. But there is one inevitable misfortune: there are some fixed stars, which for a long time are alternately visible and invisible, and at length totally disappear. Half suns would re-appear at a regular time; others that had retreated to an immense distance would at once disappear, and be concealed for a very long time: exert therefore all your resolution, madam; these stars are certainly suns which grow so dark as to be invisible to us, then resume their brightness, and afterwards are entirely extinguished. How, exclaimed the Marchioness, can a sun, a source of light, become darkened? With the greatest ease, answered I, if Descartes be in the right. He imagines that the spots on our sun, being impurities, or vapours, may grow thick, collect together, form themselves into a mass, and continue to encrust the sun till it is quite hid. If, the sun is a fire connected with a solid matter, serving as its aliment, we are not in a better condition; the solid matter may be consumed. 'Tis said we have already had a fortunate escape: the sun during several years, (the year, for instance, after the death of Cæsar;) appeared very pale; owing to the encrustation which was beginning to form. The sun had sufficient force to break and disperse it; had it continued, we should have been lost. You make me tremble, said the Marchioness. Now I know the consequences of paleness in the sun, instead of going to my glass every morning to see if _I_ am pale, I think I shall go and look whether _the sun_ is so. Take courage, madam, I replied, it requires a good deal of time to ruin a system of worlds. But, answered she, it seems as if time would inevitably effect it. I cannot take upon me to deny it, said I. The immense mass of matter which composes the universe is in continual motion, even the smallest particles of it, and since there is this motion we are in danger, for changes must happen, either slowly or rapidly, but always in a time proportioned to the effect. The ancients were so vastly wise as to imagine the heavenly bodies were of such a nature as never to alter, because they had not observed any alteration in them. Had they leisure to assure themselves of this by experience? Compared with us the ancients were young: if flowers that last but a day were to transmit their histories to each other, the first would draw the resemblance of their gardener in a certain way; after fifteen thousand ages of these flowers had elapsed, others would still describe him in the same manner. They would say; "We have always had the same gardener, the memoirs composed by our ancestors prove this to be the case; all their representations exactly apply to him; surely he is not mortal like us; no change will ever take place in him." Would the reasoning