The first volume is a good start. From memory, history, bow woods, traditional bow designs, splicing, tillering.
2nd volume, info on making bows from boards, recurves, bowyers tips.
Can't remember too much of the top of my head on Vol 3, except good info in the long term.
Volume 4, It was written later so the various bowyers come back with new opinions on their older methods, what they have changed.
Laminated wood bows.
You will want them all eventually, excellent books.