His experiments and observations led him to describe and illustrate the trout's Window of vision, a concept an understanding of which is still essential today.

Vincent Marinaro, in his classic work In the Ring of the Rise (1976), credits Ronalds with discovering and documenting this window and includes a reproduction of plate II – Optical diagrams in his book.

[4][5] In the sub-chapter "Haunts", through discussion and illustration (plate I), Alfred Ronalds introduces the idea known today as reading the water to help the angler identify the most likely locations in the stream to find trout.

[6] The real meat of Ronalds' book was Chapter IV: Of a Selection of Insects, and Their Imitations, Used in Fly Fishing.

Organized by their month of appearance, Ronalds was the first author to begin the standardization of angler names for artificial flies.

Its season depends greatly upon the state of the weather; and it will be found earlier upon the slowly running parts of the stream (such as mill dams) than on the rapid places.

His father was a successful merchant and his eldest brother, Sir Francis Ronalds, became famous for pioneering the electric telegraph.

[9] In Staffordshire, Ronalds took up the sport of fly fishing, learning the craft on the rivers Trent, Blythe and Dove.

From this hut, and elsewhere on his home rivers, Ronalds conducted experiments and formulated the ideas that eventually were published in The Fly-fisher's Entomology.

It is the textbook and in a sense the creator of the race of angler-naturalists.Ronalds is one of the major milestones in the entire literature of fly-fishing, and with his Entomology the scientific method has reached angling in full flower.

Ronalds was completely original in its content and research, setting the yardstick for all subsequent discussion and illustration of aquatic fly hatches.

Ronalds was decades ahead of his time, establishing paths that many of the greatest 20th century anglers would follow.Comparing the natural to its imitation seems an obvious approach, but no one before, or for many years thereafter, did the job effectively.