The Letter of Petrus Peregrinus

The Letter of Petrus Peregrinus on the Magnet, A.D. 1269 is a foundational scientific treatise that stands as one of the earliest known works dedicated entirely to the study of magnetism. Written by Petrus Peregrinus of Maricourt, a 13th-century French scholar and engineer, this remarkable letter—addressed to Sygerus of Foucaucourt—offers a detailed and systematic exploration of the properties and behaviors of magnets, particularly the lodestone. Composed during the height of the medieval period, the treatise is notable for its clear, methodical approach and its reliance on direct observation and experimentation, marking a significant departure from the speculative traditions of earlier natural philosophy. In this work, Peregrinus meticulously describes the construction and use of magnetic compasses, providing instructions for creating a pivoted compass needle and discussing its applications in navigation and surveying. He identifies the two poles of a magnet, explores the laws of magnetic attraction and repulsion, and investigates the phenomenon of magnetic induction. The letter also delves into the concept of magnetic declination and the alignment of the compass with the Earth's poles, laying the groundwork for later advancements in geomagnetism. Peregrinus’s treatise is divided into two parts: the first addresses the fundamental properties of magnets, including their ability to attract iron and their polarity, while the second part focuses on practical applications, such as the design of scientific instruments and the use of magnets in navigation. Throughout, the author emphasizes the importance of empirical evidence, providing detailed experimental procedures and observations that would influence generations of scientists to come. The Letter of Petrus Peregrinus on the Magnet is not only a milestone in the history of physics and technology but also a testament to the spirit of inquiry that characterized the medieval scientific tradition. Its influence can be traced through the Renaissance and into the modern era, as it inspired later scholars such as William Gilbert and contributed to the eventual development of the science of electromagnetism. This edition, made available by Project Gutenberg, includes a translation of the original Latin text, historical commentary, and illustrations that help bring Peregrinus’s pioneering work to life for contemporary readers.