“Observers are men, animals, or machines able to learn about their environment and impelled to reduce their uncertainty about the events which occur in it, by dint of learning… [We] shall examine human observers who, because we have an inside understanding of their observational process, belong to a special category. For the moment, we shall not bother with HOW an observer learns, but will concentrate upon WHAT he learns about, i. e. what becomes more certain.”

An Old Man's Thoughts on Many Things, Of Education I
Context: Could not a boy be taught the elements of astronomy at the sole cost of using his eyes and his brain; taught slowly, certainly, and not wearied with too much at once? Some would learn more than others; but all would learn something. This is real science, real knowledge, which will make a boy wiser, and probably better too. He will learn to observe carefully, and not to be deceived, as we sometimes are, by appearances.

How to Understand Politics: What the Humanities Can Say to Science (2007)

The Manly Wisdom of Will Rogers (2001)
Variant: There are three kinds of men. The one that learns by reading. The few who learn by observation. The rest of them have to pee on the electric fence for themselves.

observes it
Source: 1980s, Notes on an epistemology for living things, 1981, p.258

[NewsBank, 'Science Guy' Visits Volcano, The Chronicle, Centralia, Washington, May 18, 2009, Paula Collucci]

In der Quantenphysik dagegen bedeutet jede Beobachtung einen Eingriff in das Beobachtete; eine Zustandsveränderung am Beobachteten ist auf Grund der quantenphysikalischen Naturgesetze mit dem Beobachtungsprozess zwangslaüfig verknüpft. Also nicht ein sowieso, unabhängig von diesem Experiment vorhandener Tatbestand wird wahrgenommen, sondern wir selber rufen die Tatbestände hervor (oder: nötigen sie in bestimmter Richtung zu einer Klärung), die dann zur Wahrnehmung gelangen.
Quantenmechanische Bemerkungen zur Biologie und Psychologie, Erkenntnis, Vol. 4 (1934). p. 228.