SCIENCE OF COMMON THINGS. 63 



Swimming in fresh and salt water. Unskilful swimmers. 



to the water, renders the specific gravity of the brine 

 greater than that of fresh water, or of the egg. 



383 How do cooks sometimes ascertain if their brine be salt enough for 

 pickling f 



They put an egg into their brine. If the egg sinks, 

 the brine is not strong enough ; if the egg floats, it is. 



383 Why witt an egg sink, if the brine be not strong enough for pick- 

 ling f 



Because an egg will be the heavier ; but if as much 

 salt be added as the water can dissolve, an egg will be 

 lighter than the strong brine, and consequently float on 

 the surface. 



384 Why is it more easy to swim in the sea than in a river ? 



Because the specific gravity of salt water is greater 

 than that of fresh ; and, therefore, it buoys up the 

 swimmer better. 



385 Why do persons sink in water when they are unskilful swimmers? 



Because they struggle to keep their head out of water. 



386 Explain how this is f 



When our head is thrown back boldly into the water, 

 our mouth is kept above the surface, and we are able 

 to breathe ; but when the head is kept above the sur- 

 face of the water, the chin and mouth sink beneath it, 

 and the swimmer is suffocated. 



This may be illustrated thus : If a piece of wood be of such specific 

 gravity that only two square inches can float out of water, it is manifest, 

 that if two other inches are raised out, the two former inches must be 

 plunged in. The body (in floating) resembles this piece of wood. If 

 two square inches of our face float out of the water, we can breathe; but 

 if part of the back and crown of the head are raised above the water, the 

 lower part of the face will be depressed beneath it. 



387 Why can quadrupeds swim more easily than man f 



1. Because the trunk of quadrupeds is lighter than 

 water, and this is the greater part of them ; and 



2. The position of a beast (when swimming) is a na- 

 tural one. 



388 Why is it more difficult for a man to swim than for a beast f 



1. Because his body is more heavy in proportion 

 than that of a beast ; and 



