“After so many great men have worked on this subject, I almost do not dare to say that I have discovered the universal principle upon which all these laws are based, a principle that covers both elastic and inelastic collisions and describes the motion and equilibrium of all material bodies.
This is the principle of least action, a principle so wise and so worthy of the supreme Being, and intrinsic to all natural phenomena; one observes it at work not only in every change, but also in every constancy that Nature exhibits. In the collision of bodies, motion is distributed such that the quantity of action is as small as possible, given that the collision occurs. At equilibrium, the bodies are arranged such that, if they were to undergo a small movement, the quantity of action would be smallest.
The laws of motion and equilibrium derived from this principle are exactly those observed in Nature. We may admire the applications of this principle in all phenomena: the movement of animals, the growth of plants, the revolutions of the planets, all are consequences of this principle. The spectacle of the universe seems all the more grand and beautiful and worthy of its Author, when one considers that it is all derived from a small number of laws laid down most wisely. Only thus can we gain a fitting idea of the power and wisdom of the supreme Being, not from some small part of creation for which we know neither the construction, usage, nor its relationship to other parts. What satisfaction for the human spirit in contemplating these laws of motion and equilibrium for all bodies in the universe, and in finding within them proof of the existence of Him who governs the universe!”

As quoted by Morris Kline, Mathematics and the Physical World (1959) Ch. 25: From Calculus to Cosmic Planning, pp. 441–42.

Introductory
The Grammar of Science (1900)

Source: The Man Nobody Knows (1924), Ch. 4 : His Method

Sections I–II, p. 11–12
Natural Law; or The Science of Justice (1882), Chapter II. The Science of Justice (Continued)

Speech in reply to Senator Stephen Douglas in the Lincoln-Douglas debates http://www.bartleby.com/251/1003.html of the 1858 campaign for the U.S. Senate, at Chicago, Illinois (10 July 1858)
1850s, Lincoln–Douglas debates (1858)
Context: My friend has said to me that I am a poor hand to quote Scripture. I will try it again, however. It is said in one of the admonitions of our Lord, "As your Father in Heaven is perfect, be ye also perfect." The Saviour, I suppose, did not expect that any human creature could be perfect as the Father in Heaven; but He said, "As your Father in Heaven is perfect, be ye also perfect." He set that up as a standard; and he who did most toward reaching that standard, attained the highest degree of moral perfection. So I say in relation to the principle that all men are created equal, let it be as nearly reached as we can. If we cannot give freedom to every creature, let us do nothing that will impose slavery upon any other creature. Let us then turn this Government back into the channel in which the framers of the Constitution originally placed it. Let us stand firmly by each other. If we do not do so we are turning in the contrary direction, that our friend Judge Douglas proposes — not intentionally — as working in the traces tend to make this one universal slave nation. He is one that runs in that direction, and as such I resist him. My friends, I have detained you about as long as I desired to do, and I have only to say, let us discard all this quibbling about this man and the other man; this race and that race and the other race being inferior, and therefore they must be placed in an inferior position; discarding our standard that we have left us. Let us discard all these things, and unite as one people throughout this land, until we shall once more stand up declaring that all men are created equal. My friends, I could not, without launching off upon some new topic, which would detain you too long, continue to-night. I thank you for this most extensive audience that you have furnished me to-night. I leave you, hoping that the lamp of liberty will burn in your bosoms until there shall no longer be a doubt that all men are created free and equal.

Source: "Outlines of the Science of Energetics," (1855), p. 121; Lead paragraph: Section "What Constitutes A Physical Theory"

Preface
Philosophiae Naturalis Principia Mathematica (1687)

Principles of Social Reconstruction [Originally titled Why Men Fight : A Method Of Abolishing The International Duel], Ch. VIII : What We Can Do, p. 257
1910s
Context: It is preoccupation with possessions, more than anything else, that prevents men from living freely and nobly. The State and Property are the great embodiments of possessiveness; it is for this reason that they are against life, and that they issue in war. Possession means taking or keeping some good thing which another is prevented from enjoying; creation means putting into the world a good thing which otherwise no one would be able to enjoy. Since the material goods of the world must be divided among the population, and since some men are by nature brigands, there must be defensive possession, which will be regulated, in a good community, by some principle of impersonal justice. But all this is only the preface to a good life or good political institutions, in which creation will altogether outweigh possession, and distributive justice will exist as an uninteresting matter of course.
The supreme principle, both in politics and in private life, should be to promote all that is creative, and so to diminish the impulses and desires that center round possession.