IN POPULAR PHYSICS. 13 



10. Why will ink spilled on the edge of a booh extend 

 farther inside than if spilled on the side of the leaves? 



Because the sensible pores of the paper are short, being only 

 the thickness of a leaf, while the spaces between the leaves are 

 longer and continuous. 



11. If you should happen to spill some ink on the edge 

 of your book, ought you to press the leaves together ? 



Yes ; to make it as nearly solid as possible, until blotting pa- 

 per can be applied to remove what has not soaked into the book. 



12. Wliy can yon not mix oil and water ? 



Because there is little adhesion between them. 



13. IVliy ^vill water wet your hand while mercury will 

 not? 



Because in the former case there is strong adhesion, in the 

 latter but little. 



14. Why is a tub or pail liable to fall to pieces if not 

 filled tvith water or kept in the cellar ? 



Because the moisture dries out of the pores, and the wood 

 shrinks so as to let the hoops fall off. 



15. Name instances where the attraction of adhesion is 

 stronger than that of cohesion. 



"Wood fastened by glue will often split before the glue will 

 yield. Paper stuck with paste, and bricks with mortar, are also 

 examples. 



16. Wliy does the ivater in Fig. 18 stand higher inside 

 of the tube than next the glass on the outside ? 



There is the influence of a larger surface of glass in pro- 

 portion to the quantity of water to be lifted. 



17. Why will clothes-lines tighten and sometimes break 

 during a shower ? 



The rope absorbs water, and expands transversely. This 



shortens it with so much force as often to break it. The 



shrinking of new cloth when wet illustrates the same prin- 

 ciple. 



