. Animal locomotion, or Walking, swimming, and flying, with a dissertation on aëronautics. Animal locomotion; Aeronautics. PROGRESSION ON AND IN THE WATER. 67 motion. According to this theory the tail, when flexed or curved to make what is termed the back or non-effective stroke, is forced away from the imaginary line, its curved, concave, or biting surface being directed outwards. When, on the other hand, the tail is extended to make what is termed the effective or forward stroke, it is urged towards the ima- ginary line, its convex or non-biting surface being directed inwards (fig. 31).. Fig
. Animal locomotion, or Walking, swimming, and flying, with a dissertation on aëronautics. Animal locomotion; Aeronautics. PROGRESSION ON AND IN THE WATER. 67 motion. According to this theory the tail, when flexed or curved to make what is termed the back or non-effective stroke, is forced away from the imaginary line, its curved, concave, or biting surface being directed outwards. When, on the other hand, the tail is extended to make what is termed the effective or forward stroke, it is urged towards the ima- ginary line, its convex or non-biting surface being directed inwards (fig. 31).. Fig. 31.—Swimming of the Fish.—(After Borelli.) When the tail strikes in the direction a % the head of the fish is said to travel in the direction c h. When the tail strikes in the direction g e, the head is said to travel in the direction cb; these movements, when the tail is urged with sufficient velocity, causing the body of the fish to move in the line d c f. The explanation is apparently a satisfactory one; but a careful analysis of the swimming of the living fish induces me to believe it is incorrect. According to this, the commonly received view, the tail would experience a greater degree of resistance during the back stroke, when it is flexed and carried away from the axis of motion (d c f) than it would during the forward stroke, or when it is extended and carried towards the axis of motion. This follows, because the concave surface of the tail is applied to the water during what is termed the back or non-effective stroke, and the con- vex surface during what is termed the forward or effective stroke. This is just the opposite of what actually happens, and led Sir John Lubbock to declare that there was a period in which the action of the tail dragged the fish backwards, which, of course, is erroneous. There is this further difficulty. When the tail of the fish is urged in the direction g e, the. Please note that these images are extracted from scanned page image
Size: 2291px × 1090px
Photo credit: © Library Book Collection / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1800, bookdecade1870, booksubjectaeronau, bookyear1874
