Ira Sprague Bowen

Ira Sprague Bowen


Date of Birth
December 21, 1898
Date of Death
February 6, 1973

“Ike” Bowen studied at the Houghton Seminary and Oberlin College. As a graduate student at the University of Chicago he worked with Robert A. Millikan, whom he accompanied to the California Institute of Technology. There he served as Millikan’s assistant, taught physics, researched cosmic rays, and earned his Ph.D. with an important dissertation on heat losses in the evaporation of water from lakes. His investigation of the ultraviolet spectra of highly ionized atoms led to his identification of the mysterious “nebulium” spectral lines of gaseous nebulae as forbidden lines of ionized oxygen and nitrogen. He soon explained most of the lines of gaseous nebulae. During World War II he was in charge of photographic work on the rocket project at the Jet Propulsion Laboratory. As director of the Mt. Wilson Observatory from 1946 to 1948 and of the combined Mt. Wilson and Palomar Observatories from 1948 to 1964, he directed the completion of the 200-inch Hale telescope and 48-inch Schmidt telescope and designed many of their instruments, including a novel spectrograph. He also initiated baking photographic plates to improve their sensitivity. He continued designing astronomical instruments after his official retirement.

Presentation of Bruce medal

McKellar, Andrew, PASP 69, 105-08 (1957).

Other awards

American Academy of Arts & Sciences, Rumford Medal, 1949.
American Astronomical Society, Henry Norris Russell Lectureship, 1964.
Franklin Institute, Potts Medal, 1946.
National Academy of Sciences, Henry Draper Medal, 1942.
Optical Society of America, Frederic Ives Medal, 1952.
Royal Astronomical Society, Gold medal, 1966, presentation by T.G. CowlingQJRAS 7, 114-16 (1966).

Some offices held

Astronomical Society of the Pacific, President, 1948.

Biographical materials

Anonymous, “Dr. Ira S. Bowen New Director of the Mount Wilson Observatory,” PASP 58, 12-13 (1946).
Babcock, H.W.Biographical Memoirs of the National Academy of Science 53, 82-119.
Huntington Library, Biography accompanying inventory of scientific papers.
Osterbrock, D.E., Dictionary of Scientific Biography, 17, 95-96.
Wilson, O.C., “Retirement of Dr. Ira S. Bowen,” PASP 76, 193-96 (1964).


Aller, Laurence Hugh, QJRAS 15, 193-96 (1974).
Greenstein, Jesse L.Mercury 2, 3, 3-5 (1973).
Vaughan, Arthur H., Jr., Physics Today 26, 5, 77 & 79 (1973).
Wilson, O.C.Sky & Telescope 45, 212-214 (1973).


Caltech Archives (many)
AIP Center for History of Physics

Named after him

Bowen ratio
Lunar crater Bowen
Minor Planet #3363 Bowen


Papers, etc.

Bowen’s papers are at the Huntington Library and Caltech Archives. Excellent introduction and finding aid at the Huntington, presumably by Mt. Wilson archivist Helen S. Czaplicki. The AIP Niels Bohr Library & Archives has manuscript autobiographies of Bowen’s early life and career, some correspondence, and 1968 and 1969 oral history interviews of Bowen. He is mentioned in several other oral histories.

Other References: Historical

Bowen, I.S., “Astronomical Spectrographs: Past, Present, and Future,“ Vistas in Astronomy 1, 400-05 (1955).

Florence, Ronald, The Perfect Machine (HarperCollins, NY, 1994).

Hearnshaw, J.B., The Analysis of Starlight (Cambridge University Press, Cambridge, UK, 1986).

Hirsh, Richard F., “The Riddle of the Gaseous Nebulae,” Isis 70, 196-212 (1979).

Lewis, J.M., “The Story behind the Bowen Ratio,” Bull. Am. Meteor. Soc. 76, 2433-43 (1995) [includes brief biography].

Osterbrock, Donald E., “The Appointment of a Physicist as Director of the Astronomical Center of the World, Jour. Hist. Astron. 23, 155-65 (1992).

Sandage, AllanCentennial History of the Carnegie Institution of Washington. Vol. 1, The Mount Wilson Observatory: Breaking the Code of Cosmic Evolution (Cambridge Univ. Press, Cambridge, UK, 2004).

Struve, Otto & V. Zebergs, Astronomy in the 20th Century. (Macmillan, 1962)

Watson, Fred, “Forbidden Lines,” [poem]

Wright, Helen, Palomar, The World’s Largest Telescope, with an introduction by Ira S. Bowen (MacMillan, NY, 1952).

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Other References: Scientific

Hadfield, Robert, S.R. Williams, & I.S. Bowen, “The Magnetic Mechanical Analysis of Manganese Steel,” Proc. Roy. Soc. 98, 297-302 (1921) (pdf).

Millikan, R.A., I.S. Bowen, & R.A. Sawyer, “The Vacuum-Spark Spectra in the Extreme Ultra-Violet of Carbon, Iron, and Nickel,“ Ap.J. 53, 150-60 (1921).

R.A. Millikan & I.S. Bowen, “Extreme Ultra-violet Spectra,” Phys. Rev. 23, 1-34 (1924).

R.A. Millikan & I.S. Bowen, “The Fine Structure of the Nitrogen, Oxygen, and Fluorine Lines in the Extreme Ultra-Violet,” Philos. Mag. 48, 259-64 (1924).

Bowen, I.S. & R.A. Millikan, “The Extension of the X-ray-Doublet Laws into the Field of Optics,” Phys. Rev. 24, 209-22 (1924).

R.A. Millikan & I.S. Bowen, “Some Conspicuous Successes of the Bohr Atom and a Serious Difficulty,” Phys. Rev. 24, 223-28 (1924).

R.A. Millikan & I.S. Bowen, “The Significance of the Discovery of the X-ray Laws in the Field of Optics,” Proc. Nat. Acad. Sci. 11, 119-22 (1925).

R.A. Millikan & I.S. Bowen, “A Possible Reconciliation of Bohr’s Interpenetration Ideas with Sommerfield’s Relativistic Treatment of Electron Orbits,” Philos. Mag. 49, 923-35 (1925).

Bowen, I. S., “The Ratio of Heat Losses by Conduction and by Evaporation from any Water Surface,” Phys. Rev. 27, 779-87 (1926). Introduction of the widely used “Bowen ratio.”

Bowen, I. S., “Vacuum Spectroscopy,” J. Opt. Soc. Am. 13, 89-93 (1926).

R.A. Millikan & I.S. Bowen, “High Frequency Rays of Cosmic Origin I. Sounding Balloon Observations at Extreme Altitudes,” Phys. Rev. 27, 353-61 (1926).

Bowen, I. S. & S.B. Ingram, “Wave-Length Standards in the Extreme Ultra-Violet Spectra of Carbon, Nitrogen, Oxygen and Aluminum,” Phys. Rev. 28, 444-48 (1926).

R.A. Millikan & I.S. Bowen, “Spectral Relationships of Lines Arising from the Atoms of the First Row of the Periodic Table,” Philos. Mag. 51, 561-80 (1927).

R.A. Millikan & I.S. Bowen, “Energy Relationships and Ionization Potentials of Atoms of the First Row of the Periodic Table in All Stages of Ionization,” Proc. Nat. Acad. Sci. 13, 531-35 (1927).

Bowen, I. S., “The Origin of the Chief Nebular Lines,” PASP 39, 295-97 (1927). [reprinted in the PASP centennial volume PASP 100, 409-11 (1988) with modern commentary by Donald E. Osterbrock.]

Bowen, Ira S., “The Origin of the Nebulium Spectrum,” Nature 120, 473 (1927).

Bowen, Ira S., “The Origin of the Nebular Lines and the Structure of the Planetary Nebulae,” Ap.J. 67, 1-15 (1928) [reprinted, with commentary, in Lang, Kenneth R. & Owen Gingerich, eds., A Source Book in Astronomy & Astrophysics, 1900-1975 (Harvard Univ. Press, 1979), 581-87].

Bowen, I.S. & D.H. Menzel, “Forbidden Lines in the Flash Spectrum,” PASP 40, 332-39 (1928).

Russell, H.N. & I.S. Bowen, “Is there Argon in the Corona?” Ap.J. 69, 196-208 (1929).

Millikan, R.A. & I.S. Bowen, “The Significance of Recent Cosmic-Ray Experiments,” Proc. Nat. Acad. Sci. 16, 421 (1930).

Bowen, I.S., “The Presence of Neutral Oxygen in the Gaseous Nebulae,” Phys. Rev. 36, 600 (1930).

Millikan, R.A. & I.S. Bowen, “Similarity between Cosmic Rays and Gamma Rays,” Nature 128, 582-83 (1931).

Bowen, I.S., “Ionization of Air by γ -Rays as a Function of Pressure and Collecting Field,” Phys. Rev. 41, 24-31 (1932).

Bowen, I.S. & R.A. Millikan, “Cosmic-Ray Intensities in the Stratosphere,” Phys. Rev. 43, 695-700 (1933).

Bowen, I.S., R.A. Millikan & H.V. Neher, “New High-Altitude Study of Cosmic-Ray Bands and a New Determination of Their Total Energy Content,” Phys. Rev. 44, 246-52 (1933).

Bowen, I.S., “The Aberrations of the Concave Gratingat Large Angles of Incidence,” J. Opt. Soc. Am. 23, 313-15 (1933).

Bowen, I.S., “The Chemical Composition of the Nebulae,” PASP 46, 186-87 (1934).

Bowen, I.S., R.A. Millikan & H. Victor Neher, “A Very High Altitude Survey of the Effect of Latitude upon Cosmic-Ray Intensities And an Attempt at a General Interpretation of Cosmic-Ray Phenomena,” Phys. Rev. 46, 641-52 (1934).

Bowen, I.S., “The Spectrum and Composition of the Gaseous Nebulae,” Ap.J. 81, 1-16 (1935).

Bowen, I.S., “The Galactic Nebulae,” Scientia 59, 77-86 (1936).

Bowen, I.S., “Forbidden Lines,” Rev. Mod. Phys. 8, 55-81 (1936).

Bowen, I.S., R.A. Millikan, S.A. Korff, & H.V. Neher, “The Latitude Effect in Cosmic Rays at Altitudes up to 29,000 Feet,” Phys. Rev. 50, 579-81 (1936).

Bowen, I.S. & Everett F. Cox, “Ionization of Air by γ-Rays as a Function of Pressure and Collecting Field II ,” Phys. Rev. 51, 232-234 (1936).

Bowen, I.S., R.A. Millikan & H.V. Neher, “The Influence of the Earth’s Magnetic Field on Cosmic-Ray Intensities up to the Top of the Atmosphere,” Phys. Rev. 52, 80-88 (1937).

Bowen, I.S., R.A. Millikan & H.V. Neher, “New Evidence as to the Nature of the Incoming Cosmic Rays, Their Absorbability in the Atmosphere, and the Secondary Character of the Penetrating Rays Found in Such Abundance at Sea Level and Below,” Phys. Rev. 53, 217-23 (1938).

Bowen, I.S., R.A. Millikan & H. Victor Neher, “New Light on the Nature and Origin of the Incoming Cosmic Rays,” Phys. Rev. 53, 855-61 (1938).

Bowen, I.S., “The Image-Slicer, a Device for Reducing Loss of Light at Slit of Stellar Spectrograph,” Ap.J. 88, 113-24 (1938).

Bowen, I.S. & A.B. Wyse, “The Spectra and Chemical Composition of the Gaseous Nebulae, NGC 6572, 7027, 7662,” Lick Obs. Bull. 19, 1-16 (1939).

Bowen, I.S. & B. Eleén, “Forbidden Lines of Fe VII in the Spectrum of Nova RR Pictoris (1925),” Nature 143, 374 (1939).

Bowen, I.S. & L.T. Clark, “Hypersensitization and Reciprocity Failure of Photographic Plates,” J. Opt. Soc. Am. 30, 508-10 (1940).

Jenkins, F.A. & I.S. Bowen, “Transparency of Ocean Water,” J. Opt. Soc. Am. 36, 617ff (1946).

Bowen, I.S., “Metric Photography: Field Equipment and Operations,” in Ralph Winger & C.S. Clark, eds., i>Field Testing of Rockets, OSRD Report #254, (Caltech, Pasadena, 1946), pp. 47-89.

Bowen, I.S. & P. Swings, “The Relative Intensities of the Coronal and Other Forbidden Lines,” Ap.J. 105, 92-95 (1947).

Bowen, I.S., “The Abundance of Oxygen in the Sun,” Rev. Mod. Phys. 20, 109-12 (1948).

Bowen, I.S., “Final Adjustments and Tests of the Hale Telescope,” PASP 62, 91-97 (1950).

Bowen, I.S., “The Spectrographic Equipment of the 200-inch Hale Telescope,” Ap.J. 116, 1-7 (1952).

Bowen, I.S., “Optical Problems at the Palomar Observatory,“ J. Opt. Soc. Am. 42, 795-800 (1952).

Bowen, Ira S., “Wave Lengths of Forbidden Nebular Lines,” Ap.J. 121, 306-11 (1955) and 132, 1-17 (1960).

Bowen, I.S., “Telescopes,” A.J. 69 816-25 (1964) [Henry Norris Russell lecture].

Bowen, I.S., “Astronomical Spectrographs: Past, Present, and Future,” Vistas in Astronomy 1, 400-05 (1955).

Bowen, I.S., “The 200-inch Hale Telescope,” in Stars and Stellar Systems, ed. by G.P. Kuiper & B.M. Middlehurst, vol. 1, Telescopes, (U. of Chicago Press, Chicago, 1960), pp. 1-15.

Bowen, I.S., “Spectrographs,” in Stars and Stellar Systems, ed. by W.A. Hiltner, vol. 2, Astronomical Techniques, (U. of Chicago Press, Chicago, 1962), pp. 34-62.

Bowen, I.S., “Astronomical Optics,” Ann. Rev. Astron. & Astrophys. 5, 45-66 (1967).

Bowen, I.S., “Future Tools of the Astronomer,” QJRAS 8, 9-22 (1967) [George Darwin Lecture].

Denison, E.W., M. Schmidt, & I.S. Bowen, “An Image Tube Spectrograph for the Hale 200-inch Telescope,” in Advances in Electron Physics 28, 767-71 (1969).

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Other Works: Popularizations, History, etc.

Bowen, Ira S., “” Palomar, June 3, 1948, reprinted in Griffith Observer 12, 121-23 (1948).

Bowen, I.S., “Some New Tools of the Astronomer,” Observatory 72, 129-37 (1952) [1952 Halley Lecture].

Bowen, Ira S., “Instrumentation at the Mount Wilson and Palomar Observatories,” PASP 69, 377-84 (1957) [address on accepting the Bruce Medal].

Bowen, I.S., “Problems in Future Telescope Design,” PASP 73, 114-24 (1961).

Bowen, I.S., “Explorations with the Hale Telescope,” Astronomical Society of the Pacific Leaflets 9, 225-32 (1965) [Leaflet #429, excerpted from Science 145, 1391-98 (1964)].

Bowen, Ira S. & Bruce H. Rule, “The Palomar 60-inch Photometric Reflector,” Sky & Telescope 32, 184 (1966).