ocr: the water IS moving; the thirdis - a whirling movement after the manner of a screw, boring continually the bank andthe bed - on which it rubs, and'always gathering fresh force from the water that follows in succession, thrown back from the bank, which descends upon it from the air, and resubmerges it anew with itself at the bottom. A In these circumstances it iS interesting to compare the differences in Leonardo's treat- ment of the basic principle that the angle of incidence (the angle at which a moving force
