By Aisling O’Malley, IET Archivist

On Sunday 24th March 1940, a magnetic storm impacted the power and communication systems across North America. Reports from the time noted cases of voltage dips, the tripping of transformer banks, and severe and reactive power surges. Astronomer Seth B. Nicholson, who, at the time, described it as ‘the greatest magnetic storm of recent years’, observed disruptions to radio communications whereby static interference made announcements near incomprehensible. Nicholson also noted that a moderate aurora was detected at the Mount Wilson Observatory on the same evening.

In May of 1940, A.G. McNish, who co-led the Department of Terrestrial Magnetism at the Carnegie Institution in Washington D.C., addressed the Edison Electric Institute (EEI); McNish elucidated how the disruptions were caused during the magnetic storm in March 1940, attributing it to solar activity.

McNish referenced Norwegian scientist Kristian Birkeland’s 1913 Terrella Experiment to explain how solar winds are transmitted to earth. Birkeland theorised that the aurora borealis was the result of charged particles, solar winds, travelling across the vacuum of space to earth. To prove this theory, Birkeland devised a vacuum chamber where a suspended magnetic sphere representing earth, also known as a terrella, was bombarded with electrons to simulate a solar wind. The experiment was a success when Birkeland observed auroral displays on the sphere. The image above, featured in A.G. McNish’s address, shows Birkeland with his terrella experiment. McNish’s address is clear to point out that these were only hypothesis at the time.

McNish concluded his address to the EEI stating that regardless of the cause of magnetic storms, scientists and engineers were unable to predict or control the storms. Instead engineers had the ability to reduce the disruptions and damage caused by the magnetic storms through improved equipment. McNish also supported interdisciplinary collaboration between engineers and scientists through which the latter would provide predictions of frequency.

McNish’s address highlight the concerns that are still expressed today. An extreme solar storm in our modern world could disrupt technology integral to our lives, from satellites to power grids and could incur significant costs to the affected nation.

Access to this article can be made via the IET Library.


Magnetic Storms by A.G. McNish – Address before the Dinner Meeting of EEI Engineering Committees, Chicago Ill, May 7, 1940 – Edison Electric Institute Bulletin Vol, 8. Pages 361-365

Space Weather: Historical and Contemporary Perspectives. Louis J. Lanzerotti:

The Great Magnetic Storm of March 24, 1940, Astronomical Society of the Pacific. Seth B. Nicholson:

Space Weather Effects on Power Systems, Geomagnetic Laboratory, Geological Survey of Canada, Ottawa, Canada. D. H. Boteler:

The Northern Lights Unveiled – Kristian Birkeland’s Terrella experiment recreated:

What is the Planeterrella?

The violent solar storms that threaten Earth. Professor Chris Scott: