If your course of experimental philosophy with Abbe Nolot is over, I would have you apply to Abbe Sallier, for a master to give you a general notion of astronomy and geometry; of both of which you may know as much, as I desire you should, in six months' time. I only desire that you should have a clear notion of the present planetary system, and the history of all the former systems. Fontenelle's 'Pluralites des Mondes' will almost teach you all you need know upon that subject. As for geometry, the seven first books of Euclid will be a sufficient portion of it for you. It is right to have a general notion of those abstruse sciences, so as not to appear quite ignorant of them, when they happen, as sometimes they do, to be the topics of conversation; but a deep knowledge of them requires too much time, and engrosses the mind too much. I repeat it again and again to you, Let the great book of the world be your principal study. 'Nocturna versate manu, versate diurna'; which may be rendered thus in English: Turn Over MEN BY DAY, AND WOMEN BY NIGHT. I mean only the best editions. Whatever may be said at Paris of my speech upon the bill for the reformation of the present calendar, or whatever applause it may have met with here, the whole, I can assure you, is owing to the words and to the delivery, but by no means to the matter; which, as I told you in a former letter, I was not master of. I mention this again, to show you the importance of well-chosen words, harmonious periods, and good delivery; for, between you and me, Lord Macclefield's speech was, in truth, worth a thousand of mine. It will soon be printed, and I will send it you. It is very instructive. You say, that you wish to speak but half as well as I did; you may easily speak full as well as ever I did, if you will but give the same attention to the same objects that I did at your age, and for many years afterward; I mean correctness, purity, and elegance of style, harmony of periods, and gracefulness of delivery. Read over and over again the third book of 'Cicero de Oratore', in which he particularly treats of the ornamental parts of oratory; they are indeed properly oratory, for all the rest depends only upon common sense, and some knowledge of the subject you speak upon. But if you would please, persuade, and prevail in speaking, it must be by the ornamental parts of oratory. Make them therefore habitual to you; and resolve never to say the most common things, even to your footman, but in the best words you can find, and with the best utterance. This, with 'les manieres, la tournure, et les usages du beau monde', are the only two things you want; fortunately, they are both in your power; may you have them both! Adieu. LETTER CXXXVIII LONDON, April 15, O. S. 1751