206 ANSWERS TO PRACTICAL QUESTIONS 



the harness; but, by a steady, constantly-increased 

 draught, they will overcome the inertia of the mass. 



63. Why can a tallow candle be fired through a board? 



Because it pierces the board so quickly that the par- 

 ticles have no time to yield. Its slight cohesion, multi- 

 plied by its velocity, is greater than the cohesion of the 

 board. 



COHESION. 



46. i-io. (See Answers to these Questions under 

 Cohesion, pp. 6 and 7 of this Key.) 



1 1 . Why can glass be welded ? 



Because, like iron, it becomes viscous before melting. 



ADHESION. 



51. 1-17. (See Answers to these Questions under 

 Adhesion, pp. 7 to 9 of this Key.) 



1 8. Why does the water in Fig. 22 stand higher inside 

 of the tube than next the glass on the outside ? 



There is the influence of a larger surface of glass in 

 proportion to the quantity of water to be lifted. 



19. 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 

 principle. 



