a human body cannot sink in salt water
, though the lungs were filled as above, but from the greater specific gravity of the head. Therefore a person throwing himself on his back in salt water, and extending his arms, may easily lie so as to keep his mouth and nostrils free for breathing; and, by a slight motion of his hand, may prevent turning, if he should perceive any tendency to it.
1402. Advice to Swimmers (5)
"In fresh water if a man throw himself on his back near the surface, he cannot long continue in that situation, but by proper action of his hands on the water; if he use no such action, the legs and lower part of the body will gradually sink till he come into an upright position, in which he will continue suspended, the hollow of his breast
keeping the head uppermost
.
1403. Advice to Swimmers (6)
"But if in this erect position the head be kept upright above the shoulders, as when we stand on the ground, the immersion will, by the weight of that part of the head that is out of the water, reach above the mouth and nostrils, perhaps a little above the eyes, so that a man cannot long remain suspended in water with his head in that position.