The version in my digital garden has richer formatting and related notes and highlights.
The course of knowledge is like the flow of some mighty river, which, passing through the rich lowlands, gathers into itself the contributions from every valley. Such a river may well be joined by a mountain stream, which, passing with difficulty along the barren highlands, flings itself into the greater river down some precipitous descent, exhibiting at the moment of its union the spectacle of the utmost beauty of which the river system is capable. And such a stream is no inapt symbol of a line of mathematical thought, which, passing through difficult and abstract regions, sacrifices for the sake of its crystalline clearness the richness that comes to the more concrete studies. Such a course may end fruitlessly, for it may never join the main course of observation and experiment. But, if it gains its way to the great stream of knowledge, it affords at the moment of its union the spectacle of the greatest intellectual beauty, and adds somewhat of force and mysterious capability to the onward current.
If not anything else, this spirit (and the execution of it) is an excellent reason to write such a wonderful 32-page pamphlet with striking yet easily understandable ideas.
If you fail to find anything new in this book in regard to the fourth dimension, that is probably because this is one of those works that popularised those ideas.
As the name reveals, this book is a musing/speculation about the fourth dimension.
Hinton's four-dimensional space is an Euclidean one. This shouldn't be confused with the non-Euclidean four-dimensional space like the Minkowski's which was the basis of the Theory of Relativity. Hinton never mentioned time as the fourth dimension and it would've required a paradigm shift on Hinton's part. While it is not the spacetime we know now, it is quite an interesting system.
I liked how— example by example— Hinton built a system of fourth-dimensional space in a few pages which is consistent— complete with physical properties and consciousness, sound in its structure and extremely thought-provoking.