348 Introduction to the Study of Science 



exerts less tipping force. If the boat is constructed according 

 to a good plan and has plenty of weight on its keel, it may careen 

 with safety even when the sail is nearly touching the water. A 

 flat-bottomed boat has great stability when tipped slightly, but 

 becomes increasingly unstable when the tipping passes a certain 

 point (Fig. 118). Boats that have a weighted keel or carry 

 ballast should have inclosed air chambers to prevent sinking 

 if accidentally overturned. The mast is made as light as pos- 

 sible, but it must be strong enough to carry the sail and 

 whatever force may ordinarily be exerted upon it. 



154. Stability in other objects. Stability is not limited 

 merely to boats or bodies intended to float in water. Vehicles 

 of all kinds, such as carts, bicycles, automobiles, cars and loco- 

 motives, aeroplanes and balloons, are designed so as to have 

 the 'highest degree of stability in usual situations. The racing 

 automobile, for example, has its center of weight as low as 

 possible. 



Chairs, tables, furniture of all kinds, dishes, vases, tools, and 

 utensils must have the property of stability. If chairs tumbled 

 over when placed in their right position, they would be dis- 

 carded promptly. Buildings, however tall, must be stable; 

 and even the materials of which buildings are constructed, 

 such as brick, stone, and steel, must have in their own shape 

 maximum stability. Four-footed animals are more stable than 

 bipeds ; but bipeds have acquired a remarkable skill in main- 

 taining a certain kind of equilibrium which meets most condi- 

 tions of their environment. The equilibrium maintained by 

 these is mobile, adaptable to different conditions. It differs 

 greatly from the unstable equilibrium of such objects as the 

 tumbler doll or the bottle imp when placed so as to raise the 

 center of gravity, or of a pyramid when stood upon its apex. 

 It differs moreover from the stable equilibrium of the pyramid 

 when standing upon its base, of the tumbler doll in a vertical 

 position or of a plank lying on its broad surface. Finally it 

 differs from the indifferent or neutral equilibrium of a baseball; 



