When human activities are evaluated two things have permanence: science and history. Science is the knowledge of how the physical and biological worlds function and of their histories. It is the consequence of our learning to use instruments to read the book nature presents to us and to use our minds to form explanations out of what would otherwise be a discordant multitude of facts. It does not address why things are what we find. History is the story of how we obtained science and must tell the whole story of civilization. When the Carnegie Institution of Washington has passed from the scene, it will have left the history of a small but solid contribution.

The Institution's history can, as with other scientific organizations, be extracted from its publications, but this material lacks historical focus, and even Carnegie staff members would have difficulty obtaining a balanced picture without a significant amount of study, regardless of their familiarity with the literature of the various fields. It is the purpose of this book to perform this (very enjoyable) labor for the Department of Terrestrial Magnetism, known far and wide as DTM. It is a history intended for scientists and the scientifically literate public. The goal of the Department has been the production of science, and I construe its history to be descriptions of the advances in the sciences studied.