“If we lavishly and boldly push forward in the creation and distribution of our riches, it is hard to over-estimate the pitch of beneficial influence to which we may attain in the present. But the maintenance of such a position is physically impossible. We have to make the momentous choice between brief greatness and longer continued mediocrity.”

Source: Roll of Thunder, Hear My Cry

Introductory Lecture on Experimental Physics held at Cambridge in October 1871, re-edited by W. D. Niven (2003) in Volume 2 of The Scientific Papers of James Clerk Maxwell, Courier Dover Publications, p. 241; this has sometimes been misquoted in a way which considerably alters its intent: "in a few years, all the great physical constants will have been approximately estimated, and … the only occupation which will then be left to the men of science will be to carry these measurement to another place of decimals."
Context: This characteristic of modern experiments — that they consist principally of measurements — is so prominent, that the opinion seems to have got abroad, that in a few years all the great physical constants will have been approximately estimated, and that the only occupation which will then be left to men of science will be to carry on these measurements to another place of decimals. If this is really the state of things to which we are approaching, our Laboratory may perhaps become celebrated as a place of conscientious labour and consummate skill, but it will be out of place in the University, and ought rather to be classed with the other great workshops of our country, where equal ability is directed to more useful ends.
But we have no right to think thus of the unsearchable riches of creation, or of the untried fertility of those fresh minds into which these riches will continue to be poured. It may possibly be true that, in some of those fields of discovery which lie open to such rough observations as can be made without artificial methods, the great explorers of former times have appropriated most of what is valuable, and that the gleanings which remain are sought after, rather for their abstruseness, than for their intrinsic worth. But the history of science shews that even during the phase of her progress in which she devotes herself to improving the accuracy of the numerical measurement of quantities with which she has long been familiar, she is preparing the materials for the subjugation of the new regions, which would have remained unknown if she had been contented with the rough methods of her early pioneers. I might bring forward instances gathered from every branch of science, shewing how the labour of careful measurement has been rewarded by the discovery of new fields of research, and by the development of new scientific ideas. But the history of the science of terrestrial magnetism affords us a sufficient example of what may be done by experiments in concert, such as we hope some day to perform in our Laboratory.

As translated by William Scott Wilson. This first sentence of this passage was used as a military slogan during the early 20th century to encourage soldiers to throw themselves into battle. Variant translations:
Bushido is realised in the presence of death. In the case of having to choose between life and death you should choose death. There is no other reasoning. Move on with determination. To say dying without attaining ones aim is a foolish sacrifice of life is the flippant attitude of the sophisticates in the Kamigata area. In such a case it is difficult to make the right judgement. No one longs for death. We can speculate on whatever we like. But if we live without having attaining that aim, we are cowards. This is an important point and the correct path of the Samurai. When we calmly think of death morning and evening and are in despair, We are able to gain freedom in the way of the Samurai. Only then can we fulfil our duty without making mistakes in life.
By the Way of the warrior is meant death. The Way of the warrior is death. This means choosing death whenever there is a choice between life and death. It means nothing more than this. It means to see things through, being resolved.
I have found that the Way of the samurai is death. This means that when you are compelled to choose between life and death, you must quickly choose death.
The way of the Samurai is in death.
I have found the essence of Bushido: to die!
Hagakure (c. 1716)
Context: The Way of the Samurai is found in death. When it comes to either/or, there is only the quick choice of death. It is not particularly difficult. Be determined and advance. To say that dying without reaching one's aim is to die a dog's death is the frivolous way of sophisticates. When pressed with the choice of life or death, it is not necessary to gain one's aim.
We all want to live. And in large part we make our logic according to what we like. But not having attained our aim and continuing to live is cowardice. This is a thin dangerous line. To die without gaining one's aim is a dog's death and fanaticism. But there is no shame in this. This is the substance of the Way of the Samurai. If by setting one's heart right every morning and evening, one is able to live as though his body were already dead, he gains freedom in the Way. His whole life will be without blame, and he will succeed in his calling.

As quoted by Raymond Lonergan in Mr. Justice Brandeis, Great American (1941), p. 42.
Extra-judicial writings

Citizenship Convention, Canberra, 23 January, 1950.
Second Term as Prime Minister (1949-1966)
Source: http://www.australianquotes.com/quotes_1950-present.php

"What We Owe Our Parasites", speech (June 1968); Free Speech magazine (October and November 1995)
1960s

Source: Studies in the National Income and Expenditure of the United Kingdom, 1954, p. 286

Eragon, on entering the Vault of Souls
Inheritance (2011)

citation needed