am full of pleasant expectations. We will then complete our writing and grant all you ask. Many others besides you will find these reasonings useful, and especially those who have but recently made acquaintance with the true story of nature and those who are attached to pursuits which go deeper than any part of ordinary education. So you will do well to take and learn them and get them up quickly along with the short epitome in my letter to Herodotus .°J [] In the first place, remember that, like everything else, knowledge of celestial phenomena, whether taken along with other things or in isolation, has no other end in view than peace of mind and firm conviction. 6 We do not seek to wrest by force what is impossible, nor to understand all matters equally well, nor make our treatment always as clear as when we discuss human life or explain the principles of physics in general — for instance, that the whole of being consists of bodies and intangible nature, or that the ultimate elements of things are indivisible, or any other proposition which admits only one explanation of the phenomena to be possible. But this is not the case with celestial phenomena : these at any rate admit of manifold causes for their occurrence and manifold accounts, none of them contradictory of sensation, of their nature. " For in the study of nature we must not conform to empty assumptions and arbitrary laws, but follow the promptings of the facts ; for our life has no need now of unreason and false opinion ; our one need is untroubled existence. All things go on uninterruptedly, if all be explained by the method of