ROBERT ANDREWS MILLIKAN: BIOGRAPHY, CALCULATION OF THE ELECTRON, OTHER CONTRIBUTIONS - BIOGRAPHIES - 2025

Robert Andrews Millikan (1868-1953) was a renowned experimental physicist, as well as a notable educator and public figure in the United States during the first decades of the 20th century. Likewise, he made numerous contributions and discoveries in the fields of electricity, optics and molecular physics.

However, Millikan's great achievement was the calculation of the electron charge, which he managed to determine thanks to what is now known as the oil drop experiment.

Robert A. Millikan at the California Institute of Technology (Caltech) 1947. Source: Wikipedia commons

Today, this work is considered an ideal example of the application of the scientific method. However, beyond his research, Millikan's success was largely due to the long experience gained as a result of persistence in the study of natural phenomena.

Biography

Personal life

Robert Millikan was born on March 22, 1868 in Morrison, Illinois, and died on December 19, 1953 in San Marino, California.

When he was five years old, Millikan and his family moved to McGregor, Iowa. Two years later, the Millikans settled in Maquoketa, where Robert began his high school studies. In general, it can be established that family education was decisive in his professional life.

Similarly, his devotion and passion for his work, which was always above his personal desires and aspirations, in addition to his great intellectual honesty, led him to achieve success in science and public life.

In 1902 he married Greta Blanchard and enjoyed their honeymoon in Europe. As a result of this union, three children were born: Clark, Glenn Allen and Max Franklin.

Applied studies

In 1886 he began his studies at Oberlin College, where he learned trigonometry, analytical geometry, and Greek. He graduated in 1891 and obtained his doctorate in physics from Columbia University in 1895, being the first to do so in the department where he studied.

After receiving his doctorate, Millikan traveled to Germany (1895-1896), where he studied at prestigious universities such as Göttingen and Berlin.

During his time in Europe he related to important researchers such as the German physicist Roentgen (1845-1923), discoverer of X-rays, or the French Becquerel (1852-1903), whose studies on radioactivity were decisive in the scientific world.

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In 1910 Millikan was offered a job as an assistant at the Ryerson Laboratory at the University of Chicago, so by accepting it, he ended his tour of Europe. In this institution he worked as a teacher, holding the position until 1921.

At the University of Chicago, Millikan toiled as a researcher and educator, discovering some of his great passions in teaching.

In 1921 he left the University of Chicago to become the director of the Norman Bridge Physics Laboratory, located at the California Institute of Technology (Caltech) in Pasadena.

During his life, Millikan taught professorships in different areas of physics, was the rector of the physics laboratory at the Norman Bridge Institute and the director of Caltech.

Millikan's enthusiasm for education

Millikan was an excellent student with a great facility for teaching, so at the end of his second year at Oberlin, the professor who taught him Greek asked him to teach elementary physics.

He prepared hard for this assignment during the summer vacation of 1889. Millikan solved all the problems in the physics textbook, then went out of his way to have the students work on the problems throughout the course year.

For Millikan, the act of solving many problems was the best methodology for teaching physics. This learning system was defended by the scientist throughout his life, which is why he is also considered a great enthusiast of education.

This motivation led him to be co-author of a series of innovative texts in terms of teaching methodology. The books written by Millikan included many problems incorporating conceptual questions, which was very novel for the time.

Millikan as an advertising agent in education

Due to his determination to raise Caltech's reputation, Millikan was rated one of the great publicity agents in the field of education. This was necessary to transform the Institute into a highly prestigious center for the teaching of natural sciences and engineering.

However, he differed strongly with his colleagues on matters of politics, philosophy, and religion. Furthermore, his administrative methods were unconventional, but his personal leadership was essential for situations to take the correct course.

In conclusion, it can be stated that the influence of Millikan was a fundamental pillar in the development and training of physicists and researchers in the United States.

Millikan's investigations: electron charge and other contributions

- Estimation of electron charge

Millikan began his studies on electron charge in 1907, based on the model of the physicist HA Wilson (1874-1964). The investigation went through several stages.

The first phase consisted of ionizing the air in a cloud chamber, and then condensing the ions in a cloud. In this way, he observed and measured the fall of the cloud only under the action of gravity.

Later he evaluated the fall of an ionized cloud, but under the influence of a vertical electrical force that is superimposed on gravity. After several processes, he managed to design the oil drop experiment, which allowed him to calculate the fundamental electric charge and its mass.

This was achieved by means of equipment that dispersed oil in very small drops. These fell through a hole where they were subjected to the electric field.

Original apparatus of the oil drop. Designed by Millikan. Source: Wikipedia commons.

Through the use of special lenses a drop could be visualized and, by measuring the speed of the fall, the scientist was able to estimate the value of the mass of the electron. The experiment was repeated several times.

In this way, Millikan determined the basic load and also managed to establish its value. In 1909 he published the article where he explained the technique he used to determine the charge of the electron.

- The work in photoelectricity

His first works and publications on photoelectricity were carried out from 1907 with his student G. Winchester. The objective was to investigate whether the photoelectric current and the limiting potential depended on the temperature of the emitting metal.

During these investigations, Millikan had to deal with a number of process errors, such as the importance of cleaning metal surfaces and the danger of using sparks as a short-wave light source, as spark discharges can falsify measured potentials by inducing electrical oscillations in the device.

- The extreme ultraviolet spectrum

Millikan concluded that ultraviolet light studies using the hot sparks produced between metal electrodes were possible, thanks to his research on the potentials of these sparks.

This finding was very important to the scientific community, since all previous efforts on the short ultraviolet spectrum had been limited by its extreme absorption capacity.

But the use of a hot spark and a concave reflection grating solved the problem, as well as placing a vacuum spectrograph along the entire path of the rays.

The first results obtained with a vacuum spectrograph of this type were described by Millikan and Sawyer in 1918.

- Cosmic rays

The study of cosmic rays dates back to the early 20th century. They were experimental approaches where, through the use of electroscopes, discharge processes were measured in relation to altitude.

Millikan had difficult days in his research activities on cosmic rays. In this regard, his vigorous debates on the nature and origin of cosmic rays are highlighted. It can be established that his findings were important events in the world of science in the 1930s.

Design of the experiments

During his time in Pasadena, Millikan became actively interested in cosmic rays again. In his experiments he used electroscopes and barometers that he sent into the atmosphere with the help of sounding balloons.

These balloons reached heights of up to 11.2 and 15.2 kilometers. Instrumental values ​​were collected on ascent and descent, making it possible to determine the shock value during the procedure.

These experiments were carried out by Millikan in the spring of 1922 with IS Bowen. Their research showed that cosmic rays are more penetrating than any other known radiation.

It is decisive to indicate that, before Millikan's investigations, cosmic rays were studied only by meteorologists and specialists in radioactivity. After these works, a new field of study and research was opened for the physicists of the time.

Awards and distinctions

In 1923, Millikan received a communication announcing that he had been honored with the Nobel Prize in Physics for his research on the photoelectric effect and the charge of the electron.

Millikan attended the Third Solvay Congress in Brussels in 1921, the subject of the congress being atoms and electrons.

He received the Honoris Causa Doctorate from twenty-five universities. In addition to the Comstock Award, the Edison Medal and the Hughes Medal.

References

1. Millikan, the physicist who came to see the electron. Retrieved on December 28 from: bbvaopenmind.com
2. Du Bridge LA, Epstein PA Robert Andrews Millikan 1868-1953. A Biographical Memoir. Retrieved on December 28 from: nasonline.org
3. Reyes (1998). Some Considerations About the Role of the Experiment in the Works on Cosmic Rays of the Beginning of the 20th Century. The case of Robert Andrews Millikan. Retrieved on December 29 from: Researchgate.net
4. Du Bridge LA (1954). Robert Andrews Millikan: 1868-1953. Retrieved on December 28 from: science.sciencemag.org
5. Gullstrand A. (1924). Presentation of the Nobel Prize to Robert A. Millikan. Retrieved on December 28 from: science.sciencemag.org
6. (SA) (sf) Millikan oil-drop experiment. Retrieved on December 29 from: britannica.com