Harding, 1931

olonel Harding was one of the first of the twentieth century angler-scientists and his book is a milestone on the path of the development of modern fly fishing, the grandfather of which was Professor James Rennie. Although Harding’s work is highly original and draws on Ward's work, it is possible that it was inspired by Hewitt’s Secrets of the Salmon (1922). After dealing with refraction and reflection, Harding's chapters deal with the appearances of flies in and out of the water, the colour sense of fish and the geometry of the rise. Harding’s observations drove a coach and horses through the exact imitation school’s theory: 

They appear to assume that the trout habitually takes the floating fly after seeing it in his window and that, therefore, he sees it against a bright light. Thence, on the analogy of human vision, they argue that he must see it as a dark silhouette devoid of colour. It would appear, on the contrary, that as often as not the trout rises to the light pattern of the floating fly before ever it reaches his window.
But when the trout obviously does inspect the fly in his window, it must be remembered that his eye almost certainly magnifies largely and that, therefore, he can distinguish colour much more clearly than might be supposed. If the reader will look through a fairly strong magnifying glass at a fly against strong daylight, he will be able to distinguish its colours quite clearly, though probably unable to do so with the naked eye. When looking directly into strong sunlight, the trout probably does see only a dark silhouette, but he does not always, or even often, have to take his food in these circumstances.

Harding’s book was a monumental work, set against the standards of the day. It was the best attempt at the time at a scientifically-based fly fishing book, and the vast majority of the conclusions still hold today. His work has been carried on by Vincent Marinaro and by Goddard and Clarke.