I am wondering about the (two?) editions of the book. The first edition (1974, ISBN 0520027477) seems pretty pricey, as used copies appear to be going for $98.01 on Amazon. I assume it is out of print. The 1977 edition (ISBN 0520031830) is far cheaper at $14. Are there vast differences between the editions, and is one preferred to the other by most on the list?