SWIMMING, the art, or act, or sus taiMng the body in water, and of moving therein ; in which action the air-bladder and fins of fishes bear, a considerable part. Some have supposed; that the motion of fish in the water depends principally up on' the pectoral fins, but the contrary is easily proved by experiment ; for if the pectoral fins of a fish are cut off, and it be again put into the water, it will be found to move forward or sideways, upward or downward, as 'well •it did when it had them on. If a fish be carefully observed, while swimming in a basin of clear wa ter, it will be totted not to keep these pectoral fins constantly expanded, but only to open them at such times as it would stop or change its course ; this seeming to he their principal, if not their only use. The pectoral and ventral fins, in the common fishes of a compressed form, serve in the same manner in keep ing the fish still, and serve in scarce any other motion than that towards the bot tom ; so that this motion of the fish, which ' has been generally attributed to their fins, is almost wholly owing to their muscles, and the equipoise of their air bladder. That the use of the pectoral and ventral fins is to keep the fish steady arid upright in the water, is evident from the consequences of their loss: if they are cut off, and the fish put again into the wa ter, it cannot continue in its natural erect posture, but staggers about, and rolls from side to side. The fins of the back and anus are also of' great use to the keeping the creature in its natural posi tion, as is easily seen cutting them off, and observing the motions of the fish af terwards. Though a great deal depends on the motion of the muscles of the se veral parts of the body, in the swimming of the fish, yet the tail, and those mus cles which move the lower cart of the body, to which it is affixed, are the great instruments by which their swift motions in the water are performed. The mov ing the tail, and that part of the body to which it adheres, backward and forward, or sideways any one way, throws the whole body of the fish strongly the con trary way ; and even in swimming strait forward, the motion and direction are both greatly assisted by the vibrations of this part, as may be experienced in the motion of a boat, which, when im pelled forward, may be firmly guided by means of an oar held out at its stern, and moved in the water as occasion directs. The dorsal muscles, and those of the lower part of the body, between the anus 'and tail, are the principal that are used in the motion of this part, and these are therefore the most useful to the fish in swimming. The muscles of the belly seem to have their principal use in the contracting the belly and the air-bladder. They have been supposed of use to move the belly-fins ; but there are too many of them for such a purpose, and these fins have each its peculiar muscle, fully suffi cient to the business. The use of the tail in swimming is easily seen, by cut ting it off, and committing the' fish to the water without it, in which case it is a most helpless creature.
Brutes swim naturally, hut men attain this art by practice and industry : it con sists principally in striking alternately with the hands and feet ; which, like oars, row a person forward : he must keep his body a little oblique, that lie may the more ea sily erect his head, and keep his mouth above water. •
We shall here insert some maxims on the art of swimming that may be useful, and which are said to have been written by the late Dr. Franklin.
1. That though the legs, arms, and bead of a. human body, being solid parts, are specifically something heavier than fresh water, yet the trunk, particularlythe upper part, from its hollowness, is so much light er than water, as that the whole.olthe body, taken together, is too light to sink wholly under water, hut some part will remain above, until the lungs become filled with water ; which happens from drawing water into them instead of when a person, in the fright, attempts breathing, while the mouth and nostrils are under water. 2. That the legs and arms are specifically lighter than salt water, and will be supported by it, so that a human body would not sink in salt water, though the lungs were 611cd as above, but from the greater specific gravi ty of the head. 3.That 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 small motion of his hands, may prevent turning, if he should perceive any tendency to it. 4. That in fresh water, if a man throws 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 uses no such action, the legs and lower part of the body will gradually sink till he comes into an upright position, in which he will continue suspended, the hollow of the • breast keeping the head uppermost. 5. But if in this erect position, the head is 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 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. 6. The body continuing sus pended as before, and upright, if the head be leaned quite back, so that the face looks upwards, all the back part of the head being then under water, and its weight consequently in a great measure supported by it, the face will remain above water quite free for breathing, will rise an inch higher every inspiration, and sink as much every expiration, but never so low as that the water may come over the mouth. 7. If therefore a person, unac quainted with swimming, and falling acci dentally into the water, could have pre sence of mind sufficient to avoid struggling and plunging, and to let the body take this natural position, he might continue long safe from drowning, till perhaps help would come. For as to the clothes, their additional weight while immersed is very inconsiderable, the water supporting it ; though when he comes out of the water, he would find them very heavy indeed. The subject has within the last two or three years been investigated in Nichol son's Philosophical Journal, whence it should seem, that if a person could have sufficient presence of mind never to raise his hands above water, he could not sink.