Richard Lamb, Popular Science Monthly (1883)
“ It would be well for a beginner to observe the swimming of a frog, for undoubtedly the same method of using the legs should be adopted by man as is displayed in the model swimming of that amphibian. In analyzing the stroke of the frog, we notice that there is no vertical motion; the whole direction of the force is in a plane exactly horizontal, and is accomplished by virtually opening and closing the space between the knees—offering the sole of the foot as a resistance while kicking, and placing the feet in a position of least resistance while recovering. ”
