MUTUAL CHANGES COMMON TO ALL MATTER 69 



of level produced by lowering or raising the tube. Write out an explana- 

 tion of your observations. 



9. Ascertain that a vessel may be emptied of a liquid by means of a 

 bent tube, one end of which is at the bottom of the vessel and the other 

 at a lower level outside the vessel. The air requires to be removed from 

 the tube. Observe the conditions necessary for the commencement of 

 the operation, and explain by the use of diagrams the cause of the 

 change which goes on. 



10. Demonstrate by the use of bent tubes of the shape shown 

 in fig. 22, and containing mercury, (1) That the pressure of a liquid 

 varies as the depth ; (2) that the pressure is the same in all directions. 



11. Compare the pressure of the coal-gas in the 

 supply pipes with that of the atmosphere by noting 

 the level of liquid (water or mercury) in each branch 

 of a bent tube, one of which is exposed to the atmo- 

 sphere, the other to the coal-gas. How will the re- 

 sult be affected by a difference in the section of the 

 two branches ? 



12. Insert two tubes in two vessels containing dif- 

 ferent liquids, connect them at the top by a T-shaped 



tube, and partially exhausb the air. Measure the length of each column, 

 and calculate the relative densities of the liquids. 



13. Describe from your own observations how air enters the lungs at 

 an inspiration. 



14. Explain clearly why a body immersed in a liquid has acting upon 

 it in an upward direction a pressure, which would balance the downward 

 pressure of a volume of the liquid equal to that of the body immersed. 

 Make observations to demonstrate this statement. 



15. Observe and explain what takes place when a tube closed at one 

 end, and about 1 metre long, is completely filled with mercury and in- 

 verted over a vessel of water. Proceed cautiously at first, only partially 

 removing the thumb. 



