“[H]ow much of the fundamentals of Astronomy may be obtained with the coarsest observation with the unaided eye. …the science which is thus obtained by personal observations is vastly superior (as far as it goes) to that which is obtained by any other method. …The knowledge …inferred from actual personal observation carries with it a degree of reality and certainty, as the veritable science of external objects, which nothing else can give.”

The Philosophy of Physical Science (1938)
Context: Let us suppose that an ichthyologist is exploring the life of the ocean. He casts a net into the water and brings up a fishy assortment. Surveying his catch, he proceeds in the usual manner of a scientist to systematise what it reveals. He arrives at two generalisations: No sea-creature is less than two inches long. (2) All sea-creatures have gills. These are both true of his catch, and he assumes tentatively that they will remain true however often he repeats it.
In applying this analogy, the catch stands for the body of knowledge which constitutes physical science, and the net for the sensory and intellectual equipment which we use in obtaining it. The casting of the net corresponds to observation; for knowledge which has not been or could not be obtained by observation is not admitted into physical science.
An onlooker may object that the first generalisation is wrong. "There are plenty of sea-creatures under two inches long, only your net is not adapted to catch them." The icthyologist dismisses this objection contemptuously. "Anything uncatchable by my net is ipso facto outside the scope of icthyological knowledge. In short, what my net can't catch isn't fish." Or — to translate the analogy — "If you are not simply guessing, you are claiming a knowledge of the physical universe discovered in some other way than by the methods of physical science, and admittedly unverifiable by such methods. You are a metaphysician. Bah!"

Interview with Diane Sawyer, as quoted in "Stephen Hawking on Religion: 'Science Will Win'" on ABC World News (7 June 2010) http://abcnews.go.com/WN/Technology/stephen-hawking-religion-science-win/story?id=10830164

Universities, Actual and Ideal (1874)
1870s
Context: In an ideal University, as I conceive it, a man should be able to obtain instruction in all forms of knowledge, and discipline in the use of all the methods by which knowledge is obtained. In such a University, the force of living example should fire the student with a noble ambition to emulate the learning of learned men, and to follow in the footsteps of the explorers of new fields of knowledge. And the very air he breathes should be charged with that enthusiasm for truth, that fanaticism of veracity, which is a greater possession than much learning; a nobler gift than the power of increasing knowledge; by so much greater and nobler than these, as the moral nature of man is greater than the intellectual; for veracity is the heart of morality.

Preface
A Course of Lectures on Natural Philosophy and the Mechanical Arts (1807)

Introduction
A Treatise of Human Nature (1739-40)

Miscellaneous Works and Correspondence (1832), To Mr. Cleveland Secretary of the Admiralty (April 14, 1760)

Lecture notes of 1858, quoted in The Life and Letters of Faraday (1870) by Bence Jones, Vol. 2, p. 403
Context: We learn by such results as these, what is the kind of education that science offers to man. It teaches us to be neglectful of nothing, not to despise the small beginnings — they precede of necessity all great things. Vesicles make clouds; they are trifles light as air, but then they make drops, and drops make showers, rain makes torrents and rivers, and these can alter the face of a country, and even keep the ocean to its proper fulness and use. It teaches a continual comparison of the small and great, and that under differences almost approaching the infinite, for the small as often contains the great in principle, as the great does the small; and thus the mind becomes comprehensive. It teaches to deduce principles carefully, to hold them firmly, or to suspend the judgment, to discover and obey law, and by it to be bold in applying to the greatest what we know of the smallest. It teaches us first by tutors and books, to learn that which is already known to others, and then by the light and methods which belong to science to learn for ourselves and for others; so making a fruitful return to man in the future for that which we have obtained from the men of the past.

It has already been observed that the everyday world is rapidly assuming identity with the condition of art.
Jack Burnham (1969). "The Aesthetics of Intelligent Systems" in Edward F. Fry, ed. (1970). On the Future of Art. New York: The Viking Press, p. 103; as cited in: Edward A. Shanken. "The House That Jack Built: Jack Burnham's Concept of 'Software' as a Metaphor for Art" http://www.artexetra.com/House.html in Leonardo Electronic Almanac 6:10 (November, 1998)

Introductory
The Grammar of Science (1900)