To _tread water_, the legs must be suffered to drop in the water till the swimmer finds himself upright, he then treads downwards with his feet, occasionally paddling with the palms of his hands. The swimmer, when long in the water, will soon find himself tired, changes of action are therefore necessary; there are many which are highly advantageous to learn, such as swimming like a dog, porpoise, etc. To _swim like a dog_, he must strike with each hand and foot alternately, beginning with the right hand and foot, he must draw the hand towards the chin, and the foot towards the body, at the same time; he then must kick backwards with the foot, and strike out in a right line with the hand, and the same with the left hand and foot: the palms of the hands must be hollow, and the water pulled towards the swimmer. In _swimming like a porpoise_, the right arm is lifted entirely out of the water, the shoulder is thrust forward, and while the swimmer is striking out with his legs, he reaches forward with his hand as far as he can; his hand then falls, a little hollowed, in the water, which it grasps or pulls towards him in a transverse direction towards the other armpit. While this is going on, the legs are drawn up for another effort, and the left arm and shoulder are raised and thrust forward, as the right had previously been. When the swimmer feels tired, he may change these positions for swimming on the side. To do this, he must lower his left side and elevate his right, striking forward with his left hand, and sideways with his right, the back of the hand being in front instead of upward, the thumb side of the hand being downward so as to serve as an oar. Should the swimmer wish to turn on his back, he must keep one leg still, and embrace the water beside him with the other, and he will turn to that side. To shew the feet, he must turn himself on his back, and bend the small of it downwards, supporting himself by his hands to and fro immediately above his breast, and hold his feet above the water. Swimming under water is performed by the usual stroke, the head being kept a little downwards, and the feet struck out a little higher than when swimming on the surface. BERNARDI'S SYSTEM. _Upright swimming._--This is a new mode of swimming, introduced by Bernardi, a Neapolitan, and consists in adopting the accustomed motion of the limbs in walking. It gives great freedom to the hands and arms, affords a greater facility of breathing and of sight. It is true, that a person swimming in an upright position, advances more slowly, but as the method is more natural, the person is able to continue his course longer, and can remain with greater safety in the water.