This contribution describes—with some documentary support from Peirce's correspondence of his first and second European trips—Peirce's conception of science as a collective and co-operative activity of all those whose lives are animated by the desire to find out the truth, whose lives are animated by “an impulse to penetrate into the reason of things.” The paper has two sections: first, Peirce as an inventor and builder of research instruments around which scientific communities are formed, and, second, Peirce's own experience of cooperation within science.