CAPILLARY ATTRACTION'. 14T 



If we have a box divided bv a partition of porous clay, or any other sub- 

 stance of like nature, and place a quantity of syrup on one side, and water on 

 tlie otlier, or any otlier two liquids of different densities which freely mix with 

 one another, currents will be established between the two in opposite direc- 

 tions through the porous partition, until both are thoroughly mingled with 

 each other. 



333. If a liquid is placed in contact with a surface of 

 the body, divested of its epidermis, or outer skin, or in 

 contact with a mucous membrane, the liquid will be ab- 

 sorbed into the vessels of the body through the force of 

 endosmose. 



PRACTICAL QUESTIONS AND PROBLEMS IN HYDROSTATICS. 



1. Why are stones, gravel, and sand so easily moved hy waves and currents ? 

 Because the moving water has only to overcome about half the weight of 



the stone. 



2. Wliy can a stone which, on land, requires the strength of two men to lift it, ha 

 lifted and carried in water by one man ? 



Because the water holds up the stone with a force equal to the weight of 

 the volume of water it displaces. 



3. Why does cream rise upon milk ? 



Because it is composed of particles of oil}-, or fatty matter, which are Ughtei 

 than the watery particles of the milk. 



4. How are fishes able to ascend and descend quickly in water 7 



They are capable of changing their bulk by the voluntary distension, or 

 contractioa of a membraneous bag, or air bladder, included in their organiza- 

 tion ; when this bladder is distended, the fish increases in size, and being of 

 less specific gravitj', i.e., lighter, it rises with facilit\'; when the bladder i3 

 contracted, the size of the fish diminishes, and its tendency to sink is increased. 



5. Why does the body of a drowned porsor generally rise and float upon the surfaca 

 several days after death ? 



Because, from the accumulation of gas within the body (caused by incipient 

 putrefaction), the body becomes specifically lighter than water, and rises and 

 floats upon the surface. 



6 How are life-boats prevented from sinking ? 



They contain in tlicir sides air-tight colls, or boxes, filled with air, which by 

 their buoyancy prevent the boat from sinking, even when it is filled with water. 



7. Why does blotting-paper absorb ink ? 



The ink is drawn up between the minute fibers of the paper by capillary 

 attraction. 



8 Why will not writing, or sized paper, absorb ink ? 



Because the sizing, being a species of glue into which writing papers aro 



