„There have been applied sciences throughout the ages. … However this so-called practice was not much more than paper in nearly all of these cases, and the various applied sciences were only lacking a bagatelle, namely proper scientific practice. The applied sciences show the application of theoretic doctrines in existing events; but that is precisely what it does, it merely shows. Whereas the scientific practice autonomously puts to use these theories.“

Revue Scientifique (1871)
Variant translation: There are no such things as applied sciences, only applications of science.

Quelle: Statistical Method from the Viewpoint of Quality Control, 1939, p. 120

p, 125
"On the Harmony of Theory and Practice in Mechanics" (Jan. 3, 1856)

Preface, Tr. Bax (1883)
(1786)

Lecture on "Electrical Units of Measurement" (3 May 1883), published in Popular Lectures Vol. I, p. 73, as quoted in The Life of Lord Kelvin (1910) by Silvanus Phillips Thompson

[describing the historical causes of the modern tendency to make intellect the servant of alien interests]
The Integrity of the Intellect (July 1920)

Letter to Henrietta Jevons (28 February 1858), published in Letters and Journal of W. Stanley Jevons (1886), edited by Harriet A. Jevons, his wife, p. 101.
Kontext: You will perceive that economy, scientifically speaking, is a very contracted science; it is in fact a sort of vague mathematics which calculates the causes and effects of man's industry, and shows how it may be best applied. There are a multitude of allied branches of knowledge connected with mans condition; the relation of these to political economy is analogous to the connexion of mechanics, astronomy, optics, sound, heat, and every other branch more or less of physical science, with pure mathematics.

Preface, Tr. https://books.google.com/books?id=OCJLAAAAMAAJ Ernest Belfort Bax (1883)
Metaphysical Foundations of Natural Science (1786)

Quelle: Truth and Truthfulness (2002), p. 2

Stanza 152 (tr. Richard Fanshawe); the poet advising King Sebastian of Portugal, then eighteen years of age.
Epic poetry, Os Lusíadas (1572), Canto X
Kontext: Great Sir, let never the astonished Gall
The English, German, and Italian,
Have cause to say, the fainting Portugal
Could not advance the great work he began.
Let your advisers be experienced all,
Such as have seen the world, and studied man.
For, though in science much contained be,
In special cases practice more doth see.

Quelle: 1940s - 1950s, Theory of Experimental Inference (1948), p. 256; cited in Douglas, H.E. (2009) Science, Policy, and the Value-Free Ideal

Quelle: Science and Statistics (1976), p. 791

"By the Numbers" (May 1973), in The Tragedy of the Moon (1973), p. 190
General sources

Cited from Lord Rayleigh, The Life of Sir J. J. Thomson (1943), p. 199.
Attributed

E. J. Corey, ‎Barbara Czakó, ‎László Kürti, Molecules and Medicine (2007). Introduction

As quoted by George H. W. Bush in remarks while presenting National Medals of Science and Technology http://bushlibrary.tamu.edu/research/papers/1990/90111300.html (13 November 1990). This might be a paraphrase of statements from his introduction to "Science The Endless Frontier" (1945), rather than a direct quote. (see below)

Foreword: Two Attempts to Cheat Death (pp. 5-6)
The Immortalization Commission: The Strange Quest to Cheat Death (2011)

"On the Harmony of Theory and Practice in Mechanics" (Jan. 3, 1856)

Quelle: Systems Design of Education (1991), p. 31