Lincoln and the Calcium Light

By David J. Kent

Washington D.C.

Monday, August 16, 2021

In late August of 1864 Abraham Lincoln was still pushing research in technological advancement that might help the war effort. This interest put him in the middle of testing a calcium light between the Old Soldiers Home and the Smithsonian.

Homer Bates is best known for his post-war book, Lincoln in the Telegraph Office, in which he recounts the many visits by the President to the War Department next door to the White House. Bates recalls an incident in which a demonstration was arranged for his benefit while Lincoln was staying at what is now referred to as President Lincoln’s Cottage. Major Thomas Eckert and Bates traveled to the Soldiers Home one night while their colleagues set up a similar array in the tower of the Smithsonian Institute castle. Smithsonian Secretary Joseph Henry was also present to witness the tests.

Calcium light was not exactly new technology. Sometimes called Drummond light, and more commonly referred to as limelight, calcium lights were already in use as stage lighting for theaters and concert halls, hence the derivation of the phrase “in the limelight” for people in the public eye. The intense light is created by directing an oxyhydrogen flame at a cylinder of quicklime (calcium oxide).

According to Bates, Lincoln was greatly interested in this exhibition and expressed the opinion that the signal system of both the army and navy could and would be improved so as to become of immense value to the government.

The calcium light signaling method did go on to be of value to the war effort, as were several other signaling and coding inventions. Lincoln encouraged these developments, and in some cases like this, was intimately involved in the testing of advancements. Calcium lights were eventually replaced by arc lighting, which in turn was replaced by direct current and then alternating current. This development becomes one thread that ties Abraham Lincoln to Joseph Henry to Nikola Tesla (and Thomas Edison too).

[Originally posted on]

[Diagram courtesy of By Theresa knott (original); Pbroks13 (redraw) – Limelight_diagram.png, CC BY-SA 2.5,]