24 



Land Magnetic Obsebvations, 1914-20 



Table 6. Summary Showing the Geographical Distribution of Magnetic Stations, 1914-1920. 



' The actual number of reoccupied stations is considerably greater than enumerated since repeat stations close together 

 are counted as one locality and reoccupations of the same station at different times during 1914 to 1920 are counted but once. 



' Including stations in the Standardizing Magnetic Observatory of the Department of Terrestrial Magnetism at Wash- 

 ington; only the results with standard instruments (magnetometer C. I. W. No. 3 and earth-inductor C. I. W. No. 48) in 

 connection with tho determinations of constants and the standardization of instruments are given. 



The methods of determining longitude which are possible for observers traveling 

 under the conditions imposed by the requirements of the Department's work, depend 

 upon: (a) time-control by telegraph or cable connection with sources of reliable time- 

 si&rjals; (6) time-control by means of radio equipment sufficient for receiving time-signals 

 frdfn high-power stations; (c) transporting time by means of chronometers, or by means 



