This startling image first illustrated a lecture by Harold "Doc" Edgerton entitled "How to Make Applesauce at MIT." Moments after the apple in pierced by the .30-caliber bullet, it disentegrates completely. What is so surprising is that the entry of the supersonic bullet is as visually explosive as the exit. The duration of the flash in this photo is about 1/3 microseconds. The amount of light given off is small enough that the exposure must be made in total darkness. To trigger the flash at the proper moment, a microphone, placed a little before the apple, picks up the sound from this rifle shot, relays it through an electronic relay circuit, and then fires the microflash.
-- From Edgerton Digital Collections project, Massachusetts Institute of Technology (link: @)
* Biographical memoir (National Academy of Sciences, 2005): @