Imim XII. 



NATURAL PHILOSOPHY. 



27 



T. Where is the centre of gravity 

 light line? 



I'. In the centre of the line, so that it 

 will be maintained in a state of equilibrium ? 



T. How would you find the centre 

 of gravity of 

 a homogeneous 

 triangle ? 



P. By draw- 

 ing straight 

 lines from two 

 of its angles to 

 bisect the op- 

 posite sides, and 

 the point of in- 

 tersection, d, of 

 these two lines, 

 is the centre of gravity. Thus, the point 

 e is the centre of gravity of the line b, c, 

 and any line drawn parallel to 6 c in the 

 triangle must be bisected or divided by 

 the line a e, which proves that the cen- 

 tre of gravity lies upon the line a, e, as re- 

 gards all lines parallel to be, and, by the 

 tame reasoning it would lie in the line a b. 



T.ls the centre of grav:' 

 body always in its substance ? 



P, No ; because in a circle or ; 

 is in the centre of the circle, and in a drum 

 it is in the axis of the drum. 



[The pupil should give some other illustra- 

 tion* of the situation of the centre of ^ 

 such as coaches heavily laden upsetting: 

 attitudes of men and women dancing upon 

 the tight-rope, tendency of trees to grow in 

 a direction perpendicular to their base, &c.] 



l~>\. T. If I attempt to stand upon one 

 d fall down, is it because I cannot 

 keep the centre of gravity ? 



P. Yes; the equilibrium is not pre- 

 served, and therefore you fall over. 



HAL QUESTIONS ON LESSON XI. 

 1. What is the centre of gravity ? 



hy do bodies fall down when in- 



o one side ? 

 ... Have all bodies a centre of gravity ? 



4. How can you find the centre of 



of a body ? 



5. Give some examples of the direction 

 of the centre of gravity > 



6. Are the animal and vegetable king- 

 doms subject to its 1.. 



ive some examples of other bodies 

 being affected by it. 



LESSON XII. 



"RECAPITULATION, &c. IK Hallam had not known anything about the centre of gravity, 

 it is possible that he might have built his house in such a position tint it would have 

 fallen down, or he might have overloaded his waggons, and then there would have been 

 a probability of 'their upsetting when they ran over any urn-ven Around. The only 

 requirement for the equilibrium of any solid body is, that its centre of gravity should 

 be supported, which may be done in various ways. A body attached to an axis may 

 cither be in a state of stable, unstable, or iiuiii! lihrium, according to 



whether the centre of gravity is below, above, or within the axis. 



QUESTION& 



152. T. What do you mean by the term, 

 stable < 



d from 



its position by very *i. ,uid re- 



covers its former state, the equilibrium is 

 aid to be . 



unstable equili: 

 a body is in such a ( 

 that it may easily be disturbed, .v 

 able to recover its former state, because 



the line of direction falls outside its base, 

 it is said to be in a state of unst<il>i> 

 brium, because it must fall. When a man 

 carries a weight he must change his posi- 

 -ht and the rnan- 

 . otherwise t 1 

 of the 



body and the load would be beyo; 

 base, and he would fall. For iiut.. 

 he carries a bale of cloth, or any load upon 



