An ancient memory has surfaced.
I was about 13, and a very naive and unsophisticated 13. My father had a card for the Philadelphia Library; it enabled him to check out 12 books for three weeks. I was a voracious reader, so the deal was that he would pick out up to six books, and I could pick six.
One evening, while searching through the "to be shelved" cart for something new and different, I found the book pictured above. I was 13, therefore, a teen-ager, and I delved into it and gasped! Oh, the information it contained! I'd no idea. No idea whatsoever. I made a mental note of the call number (see, I can still remember it!). Certainly not brave enough to check the book out, on subsequent visits I would pick out my books very, very quickly and then head over to 612.6 and furtively self-educate before it was time to check out.
I don't think my father ever knew . . . .