130 QUESTIONS ON THE 



407. If the diameter of the moon be 2180 miles, and 

 her density four-fifths of that of the earth, while the 

 density of the earth is five-and-a-half times that of 

 water, what would be the length of a lever capable of 

 raising her, if inserted quite through her axis, and the 

 fulcrum be 1 100 miles distant from her centre, provided 

 a person could advantageously use a force of 2 cwt. : 

 also how long, under the above circumstances, would it 

 take to raise the moon one inch, if the moving power 

 were to travel at the rate of 50 miles an hour ? 



408. If the breadth of the back of a wedge be 6 inches, 

 what must be its length to counterpoise a weight of 10 

 tons, provided that a force of 1O cwt. be given to it? 



409. If the arm of a windlass be 18 inches, and the 

 diameter of the axis be four inches, what force will be 

 sufficient to raise a weight of 12 cwt. provided -that 

 there be but one coil of rope ?* 



410. If the diameter of the axis of a crane be eight 

 inches, and the circumference made by the moving 

 power be 10 feet, what weight will a man be able to 

 raise that can exert advantageously the force of 150 Ibs. ? 



411. If the distance between the threads of a screw 

 be a quarter of an inch, and a man can use the force of 

 1 cwt., what must be the length of the lever which forms 

 the radius of the circle of the moving power to raise a 

 weight of 20 tons ? 



GASEOUS BODIES. 



412. Define a gaseous body, and explain the difference 

 between it and vapour. 



413. By what means is it that certain bodies assume 

 a gaseous form ? 



414. Have any of the gases been at any time con- 

 densed into a liquid state 1 



415. Required the name of that gas which is the 

 chief supporter of life and light. 



* In raising a body by a wheel and axis, or windlass or other similar 

 power, if the rope after having coiled once over the axis be reverted 

 again over itself, as under certain circumstances it sometimes is two 

 or three times, it is necessary that nearly twice the thickness of the 

 rope should be added to the axis at every fresh coil. 



