“It is the province of the scientist to reveal the facts of nature as they now exist, and leave the rest to the speculation of the philosopher and the theologian.”

Source: The Number of the Beast (1980), Chapter VI : Are men and women one race?, p. 54

Knowing Yourself: The True in the False (1996)

Source: Social Amnesia: A Critique of Conformist Psychology from Adler to Laing (1975), p. 59

352
Table Talk (1569)

Source: Elements of the Philosophy of the Human Mind, 1792, p. 12

Address to the British Association in Montreal (1884)
Context: Without encroaching upon grounds appertaining to the theologian and the philosopher, the domain of natural sciences is surely broad enough to satisfy the wildest ambition of its devotees. In other departments of human life and interest, true progress is rather an article of faith than a rational belief; but in science a retrograde movements is, from the nature of the case, almost impossible. Increasing knowledge brings with it increasing power, and great as are the triumphs of the present century, we may well believe that they are but a foretaste of what discovery and invention have yet in store for mankind. … The work may be hard, and the discipline severe; but the interest never fails, and great is the privilege of achievement.

Confessio philosophi (1673)

Variant translation: One of the strongest motives that lead men to art and science is escape from everyday life with its painful crudity and hopeless dreariness, from the fetters of one's own ever-shifting desires. A finely tempered nature longs to escape from the personal life into the world of objective perception and thought. With this negative motive goes a positive one. Man seeks to form for himself, in whatever manner is suitable for him, a simplified and lucid image of the world, and so to overcome the world of experience by striving to replace it to some extent by this image. This is what the painter does, and the poet, the speculative philosopher, the natural scientist, each in his own way. Into this image and its formation, he places the center of gravity of his emotional life, in order to attain the peace and serenity that he cannot find within the narrow confines of swirling personal experience.
As quoted in The Professor, the Institute, and DNA (1976) by Rene Dubos; also in The Great Influenza (2004) by John M. Barry
1910s, Principles of Research (1918)
Context: Man tries to make for himself in the fashion that suits him best a simplified and intelligible picture of the world; he then tries to some extent to substitute this cosmos of his for the world of experience, and thus to overcome it. This is what the painter, the poet, the speculative philosopher, and the natural scientist do, each in his own fashion. Each makes this cosmos and its construction the pivot of his emotional life, in order to find in this way the peace and security which he cannot find in the narrow whirlpool of personal experience.

Nausea (1938)