The original book

The 1982 book is no longer in print, and second-hand versions are hard to come by at the price point that prof. van Dyke would have had in mind when he wrote "… needs to be inexpensive enough that it is readily accessible to students". To make his work enjoyable for all, Parabolic press has made the below pdf version of the book freely available. Of course, it is not quite the same as a hard-copy that you can flip through, so I’d encourage you to take the opportunity if you can get your hands on one of those.