Lewis Carroll is most notably known for writing the Adventures of Alice in Wonderland. I'm not sure how much of a contribution this actually was to the world of Mathematics, but the information in this text is still relevant today. The book starts out with a crude form of Truth Tables - something all computer scientists have to study to help understand conditional logic and also useful for transferring customer requirements into real working software. But he goes a little farther than is really useful before transitioning into a more algebraic format. This format appears to be an archaic precurser to modern first-order logic.
The final 100 pages of the text are problems, solutions, and a teacher's help guide. I skipped doing all of the problems. I had this class in college, and the modern notation, while not that much different, is a little easier on the eyes and more descriptive of the problem space for me.
It's a short introduction spending a little too much time on the tables, and not enough time on the first-order logical algebra. Nevertheless, it's a fun read by a famous literary giant. The entire book reads as if the Cheshire Cat was a math teacher. Example:
Our ingenious American cousins have invented a phrase to express the position of a man who wants to join one or the other of two parties—such as their two parties 'Democrats' and 'Republicans'—but can't make up his mind WHICH. Such a man is said to be "sitting on the fence." Now that is exactly the position of the red counter you have just placed on the division-line. He likes the look of No. 5, and he likes the look of No. 6, and he doesn't know WHICH to jump down into. So there he sits astride, silly fellow, dangling his legs, one on each side of the fence!
You can find a nice scanned copy of the book for free at Google Books.