/A AATUHAL PHILOSOPHY. 25 



'2. How muck wafer will it take to make a gallon of strong 

 brine ? 



A gallon. The salt does not increase the bulk of the liquid. 



3. Why can a fat man swim easier than a lean one ? 

 Because muscles and bones are heavier than fat. The speci- 

 fic gravity of a fat man is therefore less than that of a lean one. 



4. Why does the firing of a cannon over the water sometimes 

 bring to the surface the body of a drowned person ? 



One answer is given in the Philosophy. It is probable, also, 

 that the firing of the gun produces a partial vacuum, or in 

 some way takes off, for an instant, a part of the pressure of the 

 air on the water. The gases in the body would then expand 

 and bring it to the top. 



6. If we let bubbles of air pass up through a jar of water, 

 why will they become larger as they ascend? 



The pressure of the water is less as they near the top, and 

 so they expand. 



7. What is the pressure on a lock-gate 14 feet high and 10 

 feet wide, when the lock is full of water ? 



14 x 10 x 7 x 1000 oz. = 980,000 oz. = 61,250 Ibs. 



5. Will a pail of water weigh any more with a live Jish in 

 it than without ? 



If the pail were full before the fish was put in, then it will 

 make no difference, since the fish will displace its own weight 

 of water, which will run over. If the pail is only partially 

 filled, then, though the fish is upheld by the buoyancy of the 

 water, since action is equal to reaction, it adds its own weight 

 to that of the water. 



If a man and a boy were riding in a wagon, and, on com- 

 ing to the foot of a hill, the man should take up the boy in his 

 arms, would not that help the horse? 



9. If the water filtering down through a rock should collect 

 in a crevice an inch square and 250 feet high, opening at the 

 bottom into a closed fissure having 20 square feet of surface, 

 whut would be the total pressure tending to break the rock ? 



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