I had not seen this thread before, but @gunrunnerjohn's transistor circuit, evoked vivid nostalgic memories for me. It's called an astable multivibrator and was one of the first transistor projects I built in the late 1950's. (I may have also given away @gunrunnerjohn's age 
) I may have seen the design in a Popular Electronics back then.
The astable multivibrator was first invented during WW1 by two French professors Henri Abraham and Eugene Bloch using the just-invented triode vacuum tube. Its application was to help precisely measure radio frequencies and used by the French, English and U.S. military. They both continued to make other advancements radio wave engineering in later years.
The Gestapo arrested Abraham in 1943 and Bloch in 1944. Both were murdered in the Auschwitz Concentration Camp.
