“With respect to those works which, from unscientific design, give way during or immediately after their erection, I shall say little; for with all their evils, they add to our experimental knowledge, and convey a lesson, though a costly one.”

Speech to Working Men of Dundee July 14, 1875 Evoking Burn’s A Man’s A Man For A’ That - Speeches of Alexander Mackenzie during his recent visit...page 44

On his years of research in developing the electric light bulb, as quoted in "Talks with Edison" by George Parsons Lathrop in Harper's magazine, Vol. 80 (February 1890), p. 425.
Context: During all those years of experimentation and research, I never once made a discovery. All my work was deductive, and the results I achieved were those of invention, pure and simple. I would construct a theory and work on its lines until I found it was untenable. Then it would be discarded at once and another theory evolved. This was the only possible way for me to work out the problem. … I speak without exaggeration when I say that I have constructed 3,000 different theories in connection with the electric light, each one of them reasonable and apparently likely to be true. Yet only in two cases did my experiments prove the truth of my theory. My chief difficulty was in constructing the carbon filament.... Every quarter of the globe was ransacked by my agents, and all sorts of the queerest materials used, until finally the shred of bamboo, now utilized by us, was settled upon.

1920s, The Aims of Education (1929)

Letter to Robert Baldwin Hayward (1892), as quoted in Energy and Empire : A Biographical Study of Lord Kelvin (1989) by Crosbie Smith and M. Norton Wise

The Thirteenth Revelation, Chapter 35

Source: Calculating God (2000), Chapter 7 (p. 77)

Jean Vanier, Becoming Human, 2001
From books

"The Making of a Scientist," p. 11: video http://www.youtube.com/watch?v=NEwUwWh5Xs4&t=26s
What Do You Care What Other People Think? (1988)
Context: I have a friend who's an artist, and he sometimes takes a view which I don't agree with. He'll hold up a flower and say, "Look how beautiful it is," and I'll agree. But then he'll say, "I, as an artist, can see how beautiful a flower is. But you, as a scientist, take it all apart and it becomes dull." I think he's kind of nutty. … There are all kinds of interesting questions that come from a knowledge of science, which only adds to the excitement and mystery and awe of a flower. It only adds. I don't understand how it subtracts.

Source: The City of God and the True God as its Head (In Royce’s “The Conception of God: a Philosophical Discussion Concerning the Nature of the Divine Idea as a Demonstrable Reality”), p.124-5