Today I learned that Alexander Graham Bell invented a form of wireless telephony which created its signal by using a vibrating mirror to modulate light, then translated the signal back into sound by having the light shine on a substance called “lampblack.”
As far as I can tell, lampblack is basically a very fine soot.
You can read more about this in the link by ctrl-f-ing “lampblack”.
My question is, how would this substance change light into sound at all, much less change modulated light into the very sounds that produced the modulation. It seems, if I’m reading it correctly, that Bell didn’t have to do anything particularly fancy–just shine the light on the stuff and boom, a sound reproducing the original sound, audible from all around the room.
Anyone know anything about how this worked, or how it would work?
The entire paper you link to is a good read. Right at the bottom you get to what is more likely the answer. Not that the lamp black itself is expanding and contracting, but that the air in the mass of lamp black particles is heated, and thus expands and contracts. Lamp black has a silly surface area per unit volume, and such a huge surface area would be expected to help conduct more heat in a short time to the included air. Being black of course is also a great help, adsorbing as much heat as possible from the light.