The period marks a concerted effort to merge the geometrical optics framework with wave and early quantum concepts. Researchers developed practical, calculable diffraction formalisms, notably the geometrical theory of diffraction, which extended ray-based methods to edge- and aperture-induced phenomena and laid the groundwork for diffraction analysis in complex optical systems. Simultaneously, coherence and quantum-state descriptions began to permeate classical optics, foreshadowing the quantum-classical boundary that would inform holography, interferometry, and future laser technologies. Historical Significance: The advances during this window established a unified language for describing light as both rays and fields, enabling systematic treatment of diffraction, edge effects, and grating anomalies, and bridging to quantum descriptions of coherence. They provided a practical framework for diffraction calculations and coherence theory that influenced later developments in antenna theory, optical design, holography, and quantum optics.