2 THE BOTTOM OF THE SEA. 



currents of ocean below. By what miracle shall 

 the sailor be able to keep on the ti-ack to his des- 

 tined port ? By what means shall he ascertain the 

 position he occupies on the vast extent of ocean ? 

 The science of asti-onomy conies to his help, fur- 

 nishing him with the most simple and exact pro- 

 cesses, by which he may discover at any moment 

 the route he is following, and the distance which 

 yet separates him from his haven. It is by her 

 •iid that he is able to pass safely through dangers 

 almost numberless, to avoid iron-bound shores and 

 reefs, against which he would blindly hurl himself 

 to destruction if the stars did not light his uncertain 

 way. 



But it sometimes happens that the observance 

 of the heavenly bodies fails the mariner at the very 

 moment when he is most in need of their services. 

 Let us recall, for example, the numerous dangers, 

 even when the sea is quite calm, in which the ship 

 is involved which involuntarily approaches a coast 

 hidden from view by a thick curtain of fog. In 

 this and analogous cases, the seaman resorts to other 

 means for help than those furnished by astronomy. 

 Among the means most universally employed is the 

 plummet. It may be that the good ship is slowly 

 drifting on to a bank of sand or gravel which would 

 be its destruction. The lead is thrown, and the sea 



