Best thing is "illustration part" back in those days they had a brilliant talents which shows their passion of writing knowledgeable things and making it looks Good with illustration part tells they had done it with heart & soul.
I couldn't agree more. These books are real work of art. Not only the information shared on the pages are valuable, but the design as well.
Indeed. Now it's digital era where it's kind of hard to find such people with brilliant talent.