RESEARCH IN RETROSPECT:Some Biograffiti of a Journeyman Chemist.

[Figure: see text] blacksquare, square, filled Abstract Small effusive leaks in vacuum systems, as in Knudsen cells and classical molecular beam machines, are responsible for many contributions to science in the twentieth century. Beginning in the 1950s, big convective leaks have turned out to be even more powerful and versatile investigative tools. Forming supersonic free jets, they have greatly expanded molecular beam methods, become the cornerstone of cluster science and technology, rewritten the book on molecular spectroscopy, and are adding new dimension to mass spectrometry. This account is the story of one man's experiences as a bystander and participant in these developments.