How did they record sound to film camera before magnetic tape?

[Beamin]

Chapter 7 of this makes for a good introductory read: https://archive.org/details/principlesofcinema00whee

The format of that book reader is about 1000 times better then when googles archived book reader came out  several years ago and was just pages and pages of strange characters.
Flip your tablet sideways and its like a real book with yellow pages and all. Didn't know that site existed. I love reading old books that no one else would, go to the library in the town I grew up in and you will see check out dates in the 1960 and 70's then the 90's when I took them out. Best part is old books are free. Had to give up my old book habit when my eyes got bad, so maybe this is the solution! Actually best part was finding an old 20$ and $100 bill used as book marks.