“This, Herodotus, is a kind of summary and abridgment of the whole question of natural philosophy. So that, if this reasoning be allowed to be valid, and be preserved carefully in the memory, the man who allows himself to be influenced by it, even though he may not descend to a profound study of its details, will have a great superiority of character over other men. He will personally discover a great number of truths which I have myself set forth in my entire work; and these truths being stored in his memory, will be a constant assistance to him. By means of these principles, those who have descended into the details, and have studied the question sufficiently, will be able, in bringing in all their particular knowledge to bear on the general subject, to run over without difficulty almost the entire circle of the natural philosophy; those, on the other hand, who are not yet arrived at perfection, and who have not been able to hear me lecture on these subjects, will be able in their minds to run over the main of the essential notions, and to derive assistance from them for the tranquillity and happiness of life.”
This then is his letter on physics.
XXV. About the heavenly bodies he writes thus:—
EPICURUS TO PYTHOCLES, WISHING HE MAY DO WELL.
“Cleon has brought me your letter, in which you continue to evince towards me an affection worthy of the friendship which I have for you. You devote all your care, you tell me, to engraving in your memory those ideas which contribute to the happiness of life; and you entreat me at the same time to send you a simple abridgment and abstract of my ideas on the heavenly phænomena, in order that you may without difficulty preserve the recollection of them. For, say you, what I have written on this subject in my other works is difficult to recollect, even with continual study.
“I willingly yield to your desire, and I have good hope, that in fulfilling what you ask, I shall be useful too to many others, especially to those who are as yet novices in the real knowledge of nature, and to those to whom the perplexities and the ordinary affairs of life leave but little leisure. Be careful then to seize on those precepts thoroughly, engrave them deeply in your memory, and meditate on them with the abridgment addressed to Herodotus, which I also send you.
“Know then, that it is with the knowledge of the heavenly phænomena, both with those which are spoken of in contact with one another, and of those which have a spontaneous existence, as with every other science; it has no other aim but that freedom from anxiety, and that calmness which is derived from a firm belief.
“It is not good to desire what is impossible, and to endeavour to enunciate a uniform theory about everything; accordingly, we ought not here to adopt the method, which we have followed in our researches into Ethics, or in the solution of problems of natural philosophy. We there said, for instance, that there are no other things, except bodies and the vacuum, that the atoms are the principles of things, and so of the rest. In a word, we gave a precise and simple explanation of every fact, conformable to appearances.
“We cannot act in the same way with respect to the heavenly phænomena: these productions may depend upon several different causes, and we may give many different explanations on this subject, equally agreeing with the impressions of the senses. Besides, it is not here a question about reasoning on new principles, and of laying down, à priori, rules for the interpretation of nature; the only guides for us to follow are the appearances themselves; for that which we have in view is not a set of systems and vain opinions, but much rather a life exempt from every kind of disquietude.