During 1939–1947 the dominant research thrust centered on measuring nuclear magnetic moments and resonance phenomena across diverse nuclei and molecules, integrating molecular beam resonance, relaxation theory, and hyperfine interactions to quantify magnetic moments. Paramagnetic relaxation theory provided a unifying framework across physics, chemistry, and biology contexts, guiding both theory and experiment in Magnetic Resonance research. The period also showcased a broad program of exploring magnetic properties in chemical systems and solids, including diamagnetism and magnetism-enabled devices, underscoring a measurement-driven orientation of the MR field. Historical Significance: Early demonstrations of molecular beam resonance showed coherent spin manipulation and direct observation of nuclear transitions, establishing the methodological basis for Nuclear Magnetic Resonance spectroscopy and its later medical applications. The development of a formal theory of paramagnetic relaxation linked electronic-nuclear interactions to relaxation rates, providing a quantitative scaffold that shaped later Magnetic Resonance relaxation models. The emergence of Electron Spin Resonance expanded resonance techniques to electron spins in paramagnetic materials, enriching the MR toolkit and influencing subsequent spin-relaxation research.