IS 



NATURAL PHILOSOPHY. 



[Lesson VII. 



boat or carriage will fall backwards when 

 the boat is suddenly pushed from the shore, 

 or the carriage starts ; and when either of 

 them stops suddenly, the man will be thrown 

 forward--. 



75. T. "Why would the man be thrown 

 backwards when the boat or carriage 

 started ? 



P. Because his body, by obeying the 

 law of inertia, remains where it was ; but 

 his feet being pulled forwards, his bo.iy 

 falls backwards. 



76. T. If such be the case, how docs it 

 happen that the man falls forward when 

 the carriage or boat stops? 



P. Because his body has acquired the 

 same velocity as the boat or carriage, and 

 is impelled forward with that speed, while 

 his feet remain passive. 



77. T. Do you think that bodies can 

 increase or diminish their velocity? 



P. Certainly not ; they must move with 



an unchanging speed, because of them- 

 selves they cannot change the i 

 motion. An increase of its rate could 

 only be the result of some applied force, 

 and a diminution of it must be caused l>v 

 some impediment. 



GENERAL QUESTIONS ON LESSON VI. 



1. Can bodies move of themselves ' 



2. "What is the only test of the living 

 principle ? 



3. What name has been applied to pas- 

 siveness of bodies? 



4. What is inertia ? 



5. Give me some examples of inertia. 



G. Have bodies the power to arrest their 

 speed ? 



7. How are organised bodies affected" by 

 inertia ? 



8. Can bodies increase or diminish their 

 velocity ? 



LESSON VII. 



RECAPITULATION, &c. THE fact of matter being inert, and unable to pass from a 

 state of rest into one of motion, is important, and therefore when we see that a body 

 commences to move the instant we deprive it of its support, we know that it is in eon- 

 sequence of the force of gravity. But there are other phenomena in connexion with 

 gravity that require our attention : the air-balloon, the falling rain, the rising smoke, 

 are all familiar illustrations of the attraction of gravitation ; but there is also another 

 attraction to which bodies are subject a mutual attraction. For example, [Experi- 

 ment 13,] place two balls of cork or wood in a basin of water, and they will be at- 

 tracted and come into contact with each other. If, however, two balls of wood or lead 

 be suspended by strings, they cannot approach each other, without moving out of 

 the vertical line of the earth's attraction ; and as their mutual attraction cannot o\ ( 

 this, they remain at rest. Hallam learned all this by studying Natural Philosophy. It 

 was the knowledge that bodies are possessed of inertia, and the law of the attraction of 

 gravitation, that enabled him to apply the mountain-streams as a motive power for his 

 machinery ; but this he could not have done, if he had not also learned other important 

 laws in Natural Philosophy, which we shall consider hereafter. 



QUESTIONS. 



78. TVWhat is GRAVITY? 



P. It is the force which compels bodies 

 to fall. Thus, a stone or any other body 

 thrown by a person, when left to itself, will 

 fall until it reaches the earth, or any other 

 object that impedes its progress. 



79. T. Is this power limited to this 

 action, or not ? 



P. No; the actions produced by its 

 influence are various; for example the 

 rising of a piece of cork from the bottom 

 of a tumbler of water to the surface ; the 



