The books being recommended are ``Starting Forth'' and ``Thinking Forth'', both by Leo Brodie. They may be found here and here, respectively; the online edition of the former is what was read and this is the particular file for the latter.
This review concerns two excellent Forth books written by Leo Brodie. To start with, you will learn Forth if you read both of these, but those of you already knowing of Forth may want to skip the appropriately named first book being recommended. The second is a good programming book in general, although you will gain much more from it by knowing Forth beforehand.
Starting with ``Starting Forth'', the interactive Forth language is introduced by its hierarchy of definitions and most basic mechanisms; already, the beautiful and amusing illustrations that accompany the work are used for teaching to good effect. The book then introduces basic arithmetic, I/O, stack operations, the (perhaps outdated) editor, and conditionals. Following that is more material concerning numbers, primitives, basic operations, and eventually metaprogramming. Metaprogramming in Forth can be very rewarding. Ending, this book is a very good introduction to the language and should be read first, although I actually read these in the reverse order, already being familiar with Forth.
Ending with ``Thinking Forth'', this is a work that will influence your thoughts on programming in general, even if you never use Forth. The first chapter details philosophy and refinement of approach in programming, continuing the same style of pleasant illustrations from the former work recommended. The book continues in this vein, championing the idea of bottom-up programming and searching for the simplest possible approach, and giving detailed overviews of the different approaches and techniques. It is a very nice dedication to an uncommon approach to programming and I still think back to it both when writing a solution to a problem and when designing my programs. This is clearly a Forth book, but can be thought of as distilling the essence behind the language into its base concepts. If you only ever read one Forth book, read this one.