MECHANICS. 83 



ance ; but the solid of least resistance has a curve 

 resembling closely the head of a fish. 



Light and Sound. 



Light moves at the rate of 170,000 miles per 

 second. 



The mean motion of sound through the air is equal 

 to 1 1 42 feet per second. 



From Pole to Pole. 



An impression might be transmitted through the 

 ocean from pole to pole in the space of two hours 

 and fifty-five minutes. Hence probably originates 

 the intumescence of the sea which commonly pre- 

 cedes a storm : for supposing a storm to arise at the 

 distance of 50 degrees of latitude, it would not reach 

 a certain spot in less than thirty hours, whereas the 

 agitation of the waters would begin to be felt in 48-| 

 minutes. 



Gunpowder. 



Knsis^'f } ni^e 75,sulphur 10,charcoal 15=100 

 Beaume's ditto 80, 5, 15=100 



The explosive power of gunpowder depends on 

 the quantity of gas permanently generated, which 

 gas is almost entirely produced by the combustion of 

 the charcoal, the nitre being only the cause of that 

 combustion by converting the charcoal into carbonic 

 acid. The two other elements are the heat and the 

 rapidity of the inflammation, which last is secured 

 by multiplying as much as possible the intervals for 

 the passage of the flame, or by diminishing the size 

 of the grains. 



The permanently elastic fluid, generated in the 

 firing of gunpowder, is calculated by Mr. Robins to 

 be about 244 times the bulk of the powder, and that 

 the heat generated at the time of the explosion, 



