Emma. How much heavier is sea water than the fresh? Father. About one thirtieth part, which would be a guide to the master of a vessel, who was bent upon freighting it as deeply as possible. Charles. In bathing, I have often tried to swim, but have not yet been able to accomplish the task; is my body specifically heavier than the water? Father. I hope you will learn to swim, and well too; it may be the means of saving your own life, and rescuing others who are in danger of drowning: -Life is oft preserv'd By the bold swimmer in the swift illapse Of accident disastrous. THOMSON. By some very accurate experiments made by Mr. Robertson, the late librarian of the Royal Society, upon ten different persons, the mean specific gravity of the human body was found to be about 4th less than that of common river water. Charles. Why then do I sink to the bottom? I ought to swim like wood on the surface. Father. Though you are specifically lighter than water, yet it will require some skill to throw yourself into such a position as to cause you to float like wood. Charles. What is that position? Father. Dr. Franklin recommends a person to throw himself in a slanting position on his back, but his whole body, except the face, should be kept under water. And Thomson describes a youth swimming, who -through the obedient wave, At each short breathing by his lip repell'd, SUMMER Unskilful persons in the act of attempting this are apt to plunge about and struggle: by this means they take water in at their mouths and nostrils, which of itself would soon render them as heavy or heavier than the water. Moreover the coldness of the stream tends to contract the body; perhaps fear has the same tendency; all these things put together will easily account for a person sinking in the water. Emma. But if a dog or cat be thrown into the pond they seem as terrified as I should be in a like situation, yet they never fail of making their way out by swimming. Father. Of all land animals, man is, probably, the most helpless in this element. The brute creation swim naturally, the human race must acquire the art by practice. In other animals the trunk of the body is large, and their extremities small: in man it is the reverse, the arms and legs are small in proportion to the bulk of the body, but the specific gravity of the extremities is greater than that of the trunk, consequently it will be more difficult for man to keep above water than for fourfooted animals: besides, the act of swimming seems more natural to them than to us, as it corresponds more nearly to their mode of walking and running than to ours. Charles. I will try the next time I bathe to throw myself on my back according to Dr. Franklin's directions. Father. Do not forget to make your experiments in water that is not so deep as you are high by at least a foot, unless you have an experienced person with you: be. cause an unsuccessful experiment in this element, where it is but a little out of your depth, may be the last you will make. And neither your sister nor I can spare you yet. Charles. I once jumped into a part of the New River, which I thought did not ap pear deeper than you say, and I found it was over my head, but there were several persons there who soon put me in shallower water. Father. It is not so generally known as it ought be, that the depth of a clear stream of water is always one-fourth part greater than it appears to be.* Charles. If the river appear to be only three feet deep, may I reckon upon its being full four feet? Father. You must estimate it in this man ner. Remember also that if a person sink slowly in water ever so deep, a small effort will bring him up again, and if he be then able to throw himself on his back, keeping only his face above water, all will be well;t The reason of this deception is explained in our Conversations on Optics. See Vol. II. Conversation IV. It has been asserted lately, in some of our best periodical works, that if a person falling in the water, has |