308 



FIRST TEAR SCIENCE 



may know when it is safe to leave port, may be warned off 

 from dangerous shores, and, when in spite of all precau- 

 tion their vessels become wrecked, may be rescued from a 

 watery grave. 



The lighthouses have lights of different kinds and 

 colors, some fixed, some flashing, so that when unable to 



SAN FRANCISCO 

 A harbor due to depression of the coast. 



make out the coast itself, the mariner can still know his posi- 

 tion by the kind of light seen. Indeed many wireless tele- 

 graph stations are being equipped to communicate with 

 vessels at sea arid to inform them of their position, the con- 

 dition of the shore and the expected weather. Even the 

 kinds of material which form the sea floor near the shore, 

 and which may be brought up by the mariner's sounding 



