SAFEGUARDS OF THE SEA 93 



landmarks in line, or in proper relation to one 

 another, very tortuous and difficult channels 

 may be followed. 



Of course in thick or foggy weather it is 

 impossible to see landmarks or lighthouses, or 

 even beacons and buoys, and the danger of 

 vessels running on rocks or shoals would be 

 very great, unless some means were provided 

 for warning ships and letting their officers 

 know of the whereabouts of danger spots. 

 This is accomplished by means of bells, sirens 

 and horns which are sounded during thick 

 weather. Each lighthouse or lightship is pro- 

 vided with a fog signal of some sort and, in 

 order that a mariner may know which signal 

 he hears, each is arranged to sound at definite, 

 stated intervals or in a distinct manner. Many 

 of the most dangerous spots are not, however, 

 provided with either lightships or lighthouses, 

 and in such cases it is usual to establish a whis- 

 tling-buoy or a bell-buoy. The former is a 

 buoy which is provided with a horn or whistle 

 operated by the rise and fall of the waves, 

 while the bell-buoy is provided with a large 

 bell. Beneath the bell is a smooth disk upon 



