Robert Millikan: Pioneer in Electron Charge Measurement and Cosmic Ray Research

Robert Andrews Millikan (1868-1953) was a pivotal figure in the field of experimental physics, whose work significantly advanced our understanding of fundamental physical phenomena. His most renowned contribution is the precise measurement of the electron’s charge. While J.J. Thompson had identified the electron in 1897, its charge magnitude remained uncertain until Millikan’s landmark oil-drop experiment in 1909.

In his 1913 paper, Millikan reported findings based on 58 observations of charged oil drops, demonstrating that their charge was always an integral multiple of 1.6×10−191.6 \times 10^{-19}1.6×10−19 coulombs—a value remarkably close to the currently accepted figure. However, later scrutiny revealed that Millikan had carefully selected these observations from a broader set of 140, discarding those that did not align with his conclusions. Despite this, his experiment remains a cornerstone in the study of atomic physics due to its innovative methodology and significant implications.

Beyond the electron charge experiment, Millikan made substantial contributions to our understanding of cosmic rays. These high-energy particles were first identified in 1912 by Victor Hess. Through a series of meticulous observations beginning in the 1920s, Millikan demonstrated that cosmic rays originated beyond the Earth’s atmosphere, a finding that was groundbreaking at the time. However, his interpretation of the nature of these rays sparked a lengthy debate with Arthur Compton. Millikan argued that cosmic rays were electromagnetic radiation, whereas Compton insisted they were charged particles. Ultimately, Compton’s hypothesis was proven correct, but Millikan’s efforts were crucial in the advancement of cosmic ray research.

Millikan was also a prolific author, contributing to the educational landscape through several influential textbooks. His works include "A College Course in Physics" (1898), "Mechanics, Molecular Physics, and Heat" (1902), and "The Theory of Optics" (1903). His textbooks, often co-authored, were foundational in physics education, providing comprehensive resources for students and educators alike.

In summary, Robert Andrews Millikan’s contributions to physics were multifaceted and profound. His precise measurement of the electron’s charge and pioneering research on cosmic rays significantly advanced the field, while his educational texts helped shape the study of physics for generations. Despite some controversies, his legacy as a meticulous and innovative scientist endures.
Robert Millikan: Pioneer in Electron Charge Measurement and Cosmic Ray Research