138 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1918. 



gator has to depend partly on dead reckoning; also during cloudy 

 weather out of sight of land he has to depend entirely on this method 

 for his knowledge of the ship's position. Clearly then frequent de- 

 termination of the error of the compass is a most important duty. 

 In practice this error is found very simply by comparing the com- 

 pass bearing or direction of a heavenly body with its bearing, de- 

 termined by calculation if necessary, but usually taken from a table. 



The total error of the compass includes that due to actual known 

 variation of the needle and also that due to deviations caused by the 

 attraction of the iron of the ship. The former error can be found 

 from charts and easily allowed for, but the latter is variable and un- 

 certain and thus makes necessary the frequent determination of com- 

 pass correction. It is customary to reduce the deviation error as 

 much as practicable by the use of artificial magnets, as well as 

 spheres and bars of soft iron, mounted about the compass before the 

 ship leaves port, but no arrangement known effects a permanent 

 correction. 



A careful record of everything pertaining to the navigation of 

 the ship with the results of all observations and calculated positions 

 is kept in an official book, called the ship's log. Each day at noon the 

 ship's position is computed by dead reckoning from the previous 

 noon and also by astronomical observations when such are available. 

 The course and distance made good from the previous noon are then 

 computed using astronomical position if available. Finally the 

 course and distance are computed from the position of the ship at 

 noon to either the port of destination or some prominent position or 

 danger near which the vessel must pass. 



The needs of our rapidly expanding naval forces and the demand 

 of our new merchant fleet for thousands of officers have centered at- 

 tention in instruction for the preparation of navigators. The ship- 

 ping board schools, the naval schools and colleges, and also our uni- 

 versities are making a creditable effort to meet the situation. The 

 concrete result in trained men will undoubtedly fill all important 

 requirements. But in addition it is reasonable to think that progress 

 in the improvement of the art of navigation, in this country at least, 

 will be stimulated. Awkward relics of former times may be hurried 

 aside. Such obstacles as the astronomical day may be removed. 

 Certainly beneficial cooperation will follow in greater measure 

 among navigators on vessels of the Navy and the Merchant Marine 

 and those who are experts in related fields on shore. 



