Peter Newell’s innovations in book technology, while mostly not very radical, induced him to patent the designs he created, below is the first page of his patent for the Slant Book:

In the specification he writes:

… I, Peter S. Newell of Leonia, in the State of New Jersey, have invented certain new and useful Improvements in Illustrated Books and Pamphlets …
As such books have been heretofore made it has been usual to form or shape them in rectangular configuration, with the result that no, or but little, variety in the form of the books could be obtained, and the constant uniformity of such books in such forms, fails to meet the desire for change and variety which is strong in many persons, especially in children and young people. In addition to that, such monotonous form of book does not lend itself to impart any suggestion of action or motion to the design or pictorial representations which may be shown therein, so that whether the pictures represent flying or climbing upward, or sliding down hill, it is always the same rectangular form of book and page on which such motion is to be suggested or delineated.
In books made according to my invention the shape of the book itself and of the pages therein suggests the action or motion which is intended to characterize the illustration contained therein.

The pictures above show that Newell was thinking of using the peculiar shape for more varied effects, though in the end he exploited only the downhill rush in the Slant Book.

The patent for the Slant Book, along with those for a couple of 1920 figure toys (1, 2), one of which is reproduced above, is available thanks to Google Patent Search, where the full description can be read.