John D. Strong

1905 - 1992

John D. Strong (1905–1992): The Architect of Modern Experimental Optics

John Donovan Strong was a titan of 20th-century experimental physics whose work bridged the gap between theoretical optics and the practical engineering required to peer into the depths of the universe. Often described as the "experimentalist’s experimentalist," Strong’s innovations in mirror coating, infrared spectroscopy, and diffraction gratings fundamentally transformed observational astronomy and atmospheric science.

1. Biography: From the Plains to the Stars

Born on January 15, 1905, in Riverdale, Kansas, John Strong displayed an early aptitude for the mechanical and the mathematical. He earned his B.A. from the University of Kansas in 1926, followed by his M.S. (1928) and Ph.D. (1930) from the University of Michigan. His doctoral work, conducted under the guidance of E.F. Barker, focused on the infrared spectra of gases—a precursor to his lifelong fascination with the invisible portions of the electromagnetic spectrum.

Strong’s career trajectory saw him occupy pivotal roles at the world’s leading research institutions:

Caltech (1930–1942): As a Research Fellow and later Senior Fellow, he revolutionized telescope technology.
Harvard University (1942–1945): During WWII, he contributed to the war effort through the National Defense Research Committee, focusing on infrared communications and heat-seeking technologies.
Johns Hopkins University (1946–1967): He served as Professor of Physics and directed the Laboratory of Astrophysics and Physical Meteorology.
University of Massachusetts Amherst (1967–1992): He concluded his career as Professor of Physics and Astronomy, continuing his research well into his eighties.

2. Major Contributions: Engineering the Tools of Discovery

The Aluminizing Process

Before Strong, telescope mirrors were coated with silver, which tarnished rapidly and was inefficient at reflecting ultraviolet light. In the early 1930s, Strong developed a revolutionary technique for vacuum evaporation of aluminum onto glass surfaces. This process created a durable, highly reflective coating that did not tarnish. He successfully aluminized the 100-inch Hooker telescope at Mount Wilson and, most famously, designed the equipment to coat the 200-inch Hale Telescope at Palomar Observatory—then the largest in the world.

Infrared Spectroscopy and Atmospheric Physics

Strong was a pioneer in infrared (IR) instrumentation. He developed the Strong spectrometer, which allowed for high-resolution analysis of IR radiation. In 1959, he led a project using high-altitude balloons to observe the atmosphere of Venus. By lifting his instruments above the Earth’s interfering water vapor, he provided the first definitive proof of water vapor in the Cytherean atmosphere.

Diffraction Gratings

At Johns Hopkins, Strong tackled the "ruling engine"—the machine used to etch thousands of precise lines per inch onto glass to create diffraction gratings. He developed the Strong Ruling Engine, which utilized a unique "reciprocal" design to minimize errors. His gratings were world-standard, enabling spectroscopic precision that was previously unattainable.

3. Notable Publications

Strong was a prolific writer, but two works stand out as foundational texts for generations of physicists:

Procedures in Experimental Physics (1938): Co-authored with H.V. Neher, A.E. Whitford, C.H. Cartwright, and R. Hayward. Often referred to simply as "The Strong Book," it became the "bible" for experimentalists. It covered everything from glassblowing and vacuum techniques to optical polishing.
Concepts of Classical Optics (1958): A definitive textbook that integrated classical theory with the practical experimental methods Strong had pioneered.
Infrared Astronomy by Balloon-Borne Systems (1967): This documented his pioneering work in suborbital observations, laying the groundwork for modern space-based observatories like Spitzer and James Webb.

4. Awards & Recognition

Strong’s contributions were recognized by the highest bodies in the scientific community:

Frederic Ives Medal (1956): The highest award of the Optical Society of America (OSA), given for overall distinction in optics.
Franklin Institute’s Levy Medal (1939): For his work on the evaporation of metals.
President of the Optical Society of America (1959).
The Magellanic Premium (1964): Awarded by the American Philosophical Society for his contributions to navigation and astronomy.
Honorary Doctorates: Received from the University of Kansas and the University of Massachusetts.

5. Impact & Legacy

Strong’s legacy is visible in every modern reflecting telescope. The aluminizing process he perfected remains the industry standard. Furthermore, his Procedures in Experimental Physics is credited with training the generation of physicists who led the Manhattan Project and the subsequent Cold War boom in American science.

In the realm of planetary science, his balloon-borne experiments proved that sophisticated astronomical observations could be conducted from the upper atmosphere, a direct conceptual ancestor to the Hubble Space Telescope. He essentially founded the field of Infrared Astronomy, shifting the focus of the community toward wavelengths that reveal the "cool" universe (dust clouds, forming stars, and planetary atmospheres).

6. Collaborations

Strong was a consummate collaborator who thrived at the intersection of academia and industry:

George Ellery Hale: Strong worked closely with Hale to ensure the 200-inch Palomar telescope would be the most technologically advanced instrument of its time.
William M. Sinton: A student of Strong’s at Johns Hopkins, Sinton became a major figure in planetary spectroscopy.
The "Strong School": At Johns Hopkins and UMass, he mentored dozens of Ph.D. students who went on to lead labs at NASA and major aerospace firms, ensuring his "hands-on" philosophy of physics endured.

7. Lesser-Known Facts

The "Pfund" Sky Compass: During his time at Johns Hopkins, Strong helped refine the sky compass (based on the polarization of sunlight), which was used for polar navigation where magnetic compasses were unreliable.
A "Hands-On" Scholar: Unlike many theoretical professors, Strong was an expert machinist. He was known to spend as much time in the machine shop as in his office, often personally machining parts for his ruling engines.
The 1930s "Kitchen" Experiments: His first successful vacuum evaporations were performed using makeshift equipment, proving that high-level physics didn't always require massive budgets, but rather immense ingenuity.
Legacy of the "Strong Book": Even today, veteran experimentalists keep a copy of his 1938 book on their shelves; while the electronics are dated, the fundamental "shop lore" regarding materials and mechanical design remains remarkably relevant.