Elizabeth Laird: Unseen Contributor to Atomic Physics

Everything, from the page these words are written on to the eyes we read them with, is made up of atoms. That much—knowing that things are made up of other things—originated with the Greek philosopher Democritus, one of the first to postulate a theory of atomism. You likely know other major figures in the history of atomism, such as John Dalton, Michael Faraday, J.J. Thomson, and Robert Millikan. However, many lesser-known individuals contributed significantly to atomic history. Elizabeth Laird was one of them.

Laird was a Canadian physicist, born in 1874 to a minister in Ontario. Throughout her early education she excelled, finishing her studies ahead of the anticipated timeline despite health challenges and the early death of her mother. Though Laird had no exposure to physics in high school, she pursued mathematics and physics at the University of Toronto. A rumor circulated before her final year that a significant scholarship would be granted to an individual studying physics who showed promise for advancing science or industry. It was later decided internally that only men in the department would be eligible to receive the scholarship; nevertheless, Laird was set on pursuing physics.

She received a graduate fellowship at Bryn Mawr College, along with an invitation to study in Berlin, Germany. While there, Laird attended lectures given by Max Planck on theories of the electromagnetic spectrum and light. Over her career she would work alongside some of the biggest names in physics at the time.

Laird returned to the United States to chair the physics department at Mount Holyoke College in 1903. There she studied radioactivity, eventually taking leave to conduct research alongside J.J. Thomson at the Cavendish Laboratory in the United Kingdom. At Cavendish, Laird pursued research in a new direction, inspired in part by Planck’s lectures. Thomson’s iconic cathode-ray tubes weren’t being used at the time, and she took it upon herself to study whether rays could propagate through solid objects. It was already known that rays emitted within the tube could imprint on photographic plates, but Laird certified that this happened even when a sheet of fiber or paper blocked their path. The cathode rays, she found by spectroscopic analysis, emit X-rays weakly, demonstrating a further reach of the electromagnetic spectrum.

After a summer at Cavendish, Laird returned to chairing the department at Mount Holyoke. In the meantime, Albert Einstein received the 1921 Nobel Prize in Physics for discovering the photoelectric effect, the means by which excited particles are ejected from metals upon being struck by an electromagnetic ray—and their emissions included low-energy X-rays, also called soft X-rays, like those Laird studied. This discovery would prove relevant to Laird’s further research, and she took leave to study the emission of X-rays further at the University of Chicago.

In Chicago, she investigated soft X-ray propagation through solid objects, such as paper or thin sheets of silver foil, focusing on transmission and imprinting. Soft X-rays comprise the segment of the electromagnetic spectrum between extreme X-rays, such as those emitted by stellar objects, and the upper end of ultraviolet light. Laird was on the cutting edge of electromagnetic and spectroscopic research that would develop into the technology now used in X-ray imaging.

At this epoch the atom was still thought to be a solid object. Spurred on by work like Laird’s, the golden age of physics would bring a quantum mechanical approach to atomic physics that allowed scientists like Jane Dewey to take center stage in the study of wave mechanics, and the rapid discovery of new physical properties of the atom would cement the names of physical chemists such as James A. Harris in history.

This article is adapted from MJ Keller’s article “Unseen Contributors to Atomic Physics” that appeared in the AIP History Newsletter, Volume 55 (2023), Number 2.

References:

1. Laird, Elizabeth Rebecca, Autobiography, Niels Bohr Library & Archives.
2. Laird, Elizabeth and Barton, “Soft X-Rays Produced by Cathode Rays of from 200 to 600 Volts Velocities,” Phys. Rev. 15, no. 4 (1920): 297.
3. Oakes, Elizabeth H., Encyclopedia of World Scientists (New York: Facts on File, 2007).

More Unseen Contributors to Atomic Physics

Learn more about Harris and Dewey in the AIP History Newsletter, Vol. 55, No. 2, at aip.org/sites/default/files/2023-11/v55n2_2023-i1-digital-pages.pdf .