[The following is taken from Popper 1959 The Logic of Scientific Discovery (Routledge). (30. Theory and Experiment)]

　　　All these considerations are important for the epistemological theory of experiment. The theoretician puts certain definite questions to the experimenter, and the latter, by his experiments, tries to elicit a decisive answer to these questions, and to no others. All other questions he tries hard to exclude. (Here the relative independence of sub-systems of a theory may be important.) Thus he makes his test with respect to this one question '... as sensitive as possible, but as insensitive as possible with respect to all other associated questions. ... Part of this work consists in screening off all possible sources of error.'¹ But it is a mistake to suppose that the experimenter proceeds in this way 'in order to lighten the task of the theoretician',² or perhaps in order to furnish the theoretician with a basis for inductive generalizations. On the contrary, the theoretician must long before have done his work, or at least what is the most important part of his work: he must have formulated his question as sharply as possible. Thus it is he who shows the experimenter the way. But even the experimenter is not in the main engaged in making exact observations; his work, too, is largely of a theoretical kind. Theory dominates the experimental work from its initial planning up to the finishing touches in the laboratory.^*3
　　　This is well illustrated by cases in which the theoretician succeeded in predicting an observable effect which was later experimentally produced; perhaps the most beautiful instance is de Broglie's prediction of the wave-character of matter, first confirmed experimentally by Davisson and Germer.^*4 It is illustrated perhaps even better by cases in which experiments had a conspicuous influence upon the progress of theory. What compels the theorist to search for a better theory, in these cases, is almost always the experimental falsification of a theory, so far accepted and corroborated: it is, again, the outcome of tests guided by theory. Famous examples are the Michelson-Morley experiment which led to the theory of relativity, and the falsification, by Lummer and Pringsheim, of the radiation formula of Rayleigh and Jeans, and of that of Wien, which led to the quantum theory. Accidental discoveries occur too, of course, but they are comparatively rare. ... (Popper 1959: 107-108)

　¹ H. Weyl, Philosophie der Mathematik und Naturwissenschaft, 1927, p. 113; English Edition: Philosophy of Mathematics and Natural Science, Princeton, 1949, p. 116.
　² Weyl, ibid.
　^*3 I now feel that I should have emphasized in this place a view which can be found elsewhere in the book (for example in the fourth and the last paragraphs of section 19). I mean the view that observations, and even more so observation statements and statements of experimental results, are always interpretations of the facts observed; that they are interpretations in the light of theories. This is one of the main reasons why it is always deceptively easy to find verifications of a theory, and why we have to adopt a highly critical attitude towards our theories if we do not wish to argue in circles: the attitude of trying to refute them.
　^*4 The story is briefly and excellently told by Max Born in Albert Einstein, Philosopher-Scientist, edited by P A. Schilpp, 1949, p. 174. There are better illustrations, such as Adam's and Leverrier's discovery of Neptune, or that of Hertzean waves.