152 ELEMENTS OF GENERAL SCIENCE 



168. Harbors. A good harbor is a necessity for any city 

 which carries on commerce by water. There must be some 

 place where vessels may lie in quiet water while unloading 

 or taking on cargo. This purpose was served from the first 

 by the Chicago River. The river was a shallow stream, and as 

 lake vessels increased in size it was necessary to deepen the 

 river and to make other improvements. Since the harbor is 

 open to all vessels, it is the business of the government to 

 make these improvements. The main stream and many miles 

 on both its branches have been dredged until they have now 

 a depth of at least 20 feet throughout, and the lake steamers 

 can land alongside at any point. The river has not proved 

 sufficient for the commerce of the city, and therefore a harbor 

 with more room has been constructed by building great break- 

 waters at some distance from the shore in front of the city. 

 These breakwaters check the force of the waves and produce 

 a fairly quiet area behind them in which vessels can lie 

 in security. Such artificial harbors must be constructed at 

 many ports. 



169. Lights, buoys, and life-saving stations. Lighthouses 

 are placed at the harbor entrances and at other places, to 

 guide the master of a vessel safely into the harbor or to warn 

 him of danger. Certain important lighthouses are equipped 

 with foghorns, which are sounded at intervals of a number of 

 seconds during rainy or foggy weather, when the lighthouse 

 may not be visible. Obstructions, shallow places, and other 

 dangers are commonly marked by buoys of different shapes 

 and colors. 



Life-saving stations are maintained at many places. Each 

 station is in charge of a crew of trained and experienced men 

 and is equipped with boats and other special apparatus for the 

 saving of life in case of wreck or other accident. It is better, 

 however, to prevent wrecks than to save life after a wreck, 

 and one of the measures taken for this purpose consists 

 in maintaining storm-signal stations, which are frequently 



