OK, PLAIN TEACHING. 



5 



by the war of elements. Near 

 the shore, however, the waters 

 being shallow, the waves fall upon 

 resisting banks and rocks, then 

 they are broken, and lashed into 

 foam, and fishes and water plants, 

 algae, becoming involved in the 

 stormy margin of the coast, are 

 cast upon the shore. Waves are 

 said to "roll mountains high," 

 but those of the greatest magni- 

 tude rarely exceed thirty feet 

 from the hollow of the depressed 

 wave to the crest of the elevated 

 one. The water forming waves 

 does not advance, but the motion 

 is imparted to succeeding bodies 

 of water. Only a little of the 

 spray, or the rippled water impel- 

 led by the wind, moves forward. 

 But the ocean is in perpetual 

 movement. Not only do changes 

 of temperature, and the flow of 

 rivers, affect its condition, but, 

 from millions of miles away, in 

 the far depths of space, the hea- 

 venly bodies attract it, and form 

 one great primary wave, which is 

 for ever moving. # 



The depth of the ocean is liable 

 to immense variations, and in some 

 instances has never been ascer- 

 tained. The measurement 

 of the depths of the sea is 

 l called taking soundings ; a 

 heavy lead, 5, attached to a 

 strong thin line,6, is sunk in 

 the water until it touches 

 the bottom. Soundings 

 ^ i | taken in th e Atlantic Ocean 

 I have shown a depth of 

 18,000 feet, or about three 

 112. miles and a-half; soundings 

 in the Southern Atlantic, 

 to the west of the Cape of Grood 



• Sec the " Walk by the Sea Shore." 



Hope, showed a depth of 21,000 

 feet, or more than five miles, and 

 then the bottom was not found. 

 At a point 300 miles from the 

 Bermudas, 5700 fathoms of line 

 were paid out (nearly six and a- 

 half miles') and no bottom found. 

 Near the same parallel, bottom 

 was found ; at less than half the 

 above depth. Midway between 

 the Islands of Tristan d'Acunha 

 and the mouth of the Rio de la 

 Plata, the bottom was reached at 

 a depth of 7706 fathoms, equal to 

 46,236 (more than 46,000) feet, 

 or eight miles and three-quarters. 

 The time occupied by running 

 out the line was nearly three 

 hours. The average depth of the 

 sea on the coast of England is 

 estimated at aboi^t 120 feet ; on 

 the coast of Scotland, 360 feet ; 

 on the western coast of Ireland, 

 2000 feet. Soundings with the 

 lead cannot be fully relied upon, 

 on account of frequent currents, 



sometimes running in opposite 

 directions, 9, 9, at different depths, 



