The Japanese theoretical physicist Ryogo Kubo made remarkable contributions to statistical mechanics and condensed matter physics, amongst which his name is most widely associated with the linear response theory. Despite his importance in the history of modern physics, however, historians have paid him little attention. Using his unpublished manuscripts in a newly organized archive, this paper examines his studies and research up to the end of World War II. Influenced by his brother Masaji Kubo, a physical chemist, and the milieu at Tokyo Imperial University, he became interested in theoretical approaches to properties of matter and worked on dipolar gases and resistance in metals. After graduation, he studied three different phenomena—relaxation, melting, and rubber elasticity—by applying the method of eigenvalue problems. He was also involved in wartime research on noctovision and worked on photoemission in semiconductors. This paper also identifies two distinct focuses in his early research that persisted in his work after the war: solid-state physics and statistical mechanics in today’s terminology. Reconstructing Kubo’s formative years is instrumental for constructing a historiography of a key aspect of modern Japanese physics, namely, how the science of matter evolved before and during the war.

日本理论物理学家久保凉吾（Ryogo Kubo）为统计力学和凝聚态物理学做出了杰出贡献，其中他的名字与线性响应理论联系最为广泛。尽管他在现代物理学史上很重要，但是历史学家对他的关注却很少。本文使用他在新组织的档案中未出版的手稿，考察了他对第二次世界大战结束之前的研究。在物理化学家的兄弟久保雅治（Masaji Kubo）和东京帝国大学的环境的影响下，他对物质性质的理论方法产生了兴趣，并从事偶极气体和金属电阻的研究。毕业后，他通过使用特征值问题的方法研究了三种不同的现象-松弛，熔化和橡胶弹性。他还参与了有关夜视技术的战时研究，并从事半导体的光发射工作。本文还确定了战后他坚持的早期研究中的两个不同重点：当今术语中的固态物理学和统计力学。重建久保的成长年景有助于构建现代日本物理学一个重要方面的史学，即史实在战前和战争期间如何发展。