Volume S was soooo big! Gravdir, those are the very ones, and your picture brought a palpable wave of nostalgia. I spent a lot, really a lot of time between the covers of those doorways to the universe. I remember that time as fondly as any childhood memory I have.
I should also add that I spend a lot of time in the dictionary, though I can't recall exactly which one. It was big, but not too big to hold in my lap. It wasn't the OED, for example. The dictionary? you say? Yes, whenever I didn't know what a word meant in my reading, and there were countless times that happened, I learned to look it up in the dictionary. Dad said to look it up in the dictionary. I know, because asking Dad "what does xyz mean?" **always** produced the answer "look it up".
Gee. thanks Dad, I sure am glad I have you here to teach me stuff. I said in my (mind) fit of pre-adolescent pique. But I still contend I have grounds for complaining when I got that same answer to the question "Dad, how do you spell xyz?". Still didn't work. "Look it up."
And a trip to the dictionary was never rewarded with learning just one word, never. One word would lead to another interesting word, and that would lead to another interesting definition, lather, rinse, repeat. The dictionary and the encyclopedia reinforced each other, reading one showed me stuff I didn't know that I had to look up in the other one, etc, etc. A very virtuous and verbose cycle.
Thanks Dad!