Lesson VI.] 



MEGHAN 



81 



GENERAL QUESTIONS ON LESSON V. 



1. How should we act when a lever is 

 required to possess very great mechanical 

 power ? 



_'. Hew is the action of a system of 

 levers calculated ? 



3. What is a compound lever? 



4. Is the power of a compound lever 

 capable of being increased or diminished? 



5. Explain what is meant by the power 

 of a machine. 



6. State how the variation in the centre 

 of gravity of a lever affects its action. 



LESSON VI. 



THERE cannot be a doubt that science is vastly indebted to the lever, but yet it* use 

 is limited, and its action intermitting; and, therefore, we must look for further 

 mechanical assistance, and, fortunately, we have not much trouble in obtaining it 

 You remember that Ferguson tried many experiments with levers ; and then he thought 

 that, by pulling round a wheel, the weight might be raised to any height by tying a 

 rope to the weight, and winding the rope round the axle of the wheel ; and, when he 

 tried the effect of his theory, he found that it was correct. GRANDFATHI.K WHITKJIEAD 

 wishes his pupils to imitate Ferguson, and make some machines for themselves, and 

 try the mechanical experiments he is going to perform for them. Ferguson tells us 

 that, by means of a turning-lathe which his f.ither had, and sometimes used, 

 and a little knife, he was enabled to make wheels, and other things nee 

 for his purpose. It is not every one that can avail themselves of a turning- 

 lathe; but they may get some old cotton reels, and, by sawing off the two ends 

 and glueing them together (as in the annexed diagram,) very tolerable wheels 

 for pulleys may be made ; and by means of them, a few pieces of boar.: 

 stout wire, a pair of pliers, a knife, and a saw, many excellent temporary blockt 

 may be constructed. In the frontispiece is an illustration of a man drawing 

 a bucket up a well. The principle is the same as the wheel and axle, although the 

 .' i> only one of the many varieties of this mechanical appli.uu < Ciitt 



so many important advantages. 



QUESTIONS. 



T. What is the wheel and axle ? 

 P. A more complicated form of thft 

 lever, contiting of a wheel or large flat 

 T, with a smaller cylinder passing 

 through its centre, which has received the 

 t axle. 



66. T. Is the wheel fixed to the axle, 



P. The wheel is sometimes fixed to its 

 that both r about 



the same centre, a i 

 its axle ; but wr 1. r tin- 







ver received 

 any other name ? 



it has sometimes been called 

 "the perpetual lever," and son 



68. T. Did you not tell me that a lever 

 moved upon or about a fulcrum, or a fixed 

 axis? 



/'. Yes; and I have given you 



to prove that it nrnim upon or 



fulcrum ; and shall now be able to 



show that it moves about a fixed axis 



i 31. Take a 

 of wood, bore a hole in its centre (a), and 



