SCIENCE OF COMMON THINGS. 203 



Mechanical force of steam. Comparison of steam power and animal power. 



1346 What substance furnishes the means of calling the powers of coal 

 into activity ? 



Water. 



1347* How much water will two ounces of coal evaporate t 



About a pint. 



1348 How much steam will this produce f 



Two hundred and sixteen gallons. 



1340 How much mechanical force can this steam exert t 



It can raise a weight of thirty-seven tons to the 

 height of one foot. 



1350 What amount of force can a man exert when applying his 

 strength to the best advantage through the help of machinery f 



It has been found by experiment, that a man work- 

 ing on a tread-mill continuously for eight hours, will 

 elevate one and a half millions of pounds to the height 

 of one foot. 



1351 With how much coal will a well constructed steam-engine perform 

 the same labor ? 



With the expenditure of a pound and a half. 



1352 How much coal then would be equivalent to the average power of 

 an able-bodied man during his active life, supposing him to work for twenty 

 years at Hie rate of eight hours per day ? 



The consumption of about four tons of coal would 

 evolve in a steam-engine fully as much power. 



1353 The great pyramid of Egypt is five hundred feet high, and weighs 

 twelve thousand seven hundred and sixty millions of pounds. Herodotus 

 states that in constructing it one hundred thousand men were constantly 

 employed for twenty years. With how much coal could all the materials of 

 this pyramid be raised to their present position from the ground ? 



With the expenditure of four hundred and eighty 

 tons of coal. 



