PROPOSED MAGNETIC SURVEY OF NORTH PACIFIC OCEAN. 27 I 



at San Francisco ; so that, if it is found that the method pursued is 

 not the best, the work can readily be terminated or modified. Each 

 circuit is so planned as to contribute the maximum results with the 

 highest efficiency. 



From letters received in response to inquir}^ (two of the letters are 

 appended) it would appear that the entire work of observation and 

 reduction can be accomplished in three years. The cost per month of 

 the field work, inclusive of all expenses and services, will approximate 

 $1,500. Counting eight months of continuous service per annum, 

 the total annual outlaj' would be about $12,000. This sum can be 

 provided for out of the allotments for field-work available to the 

 Department of International Research in Terrestrial Magnetism if 

 the annual grant to this department be made $25,000, as per the 

 original plan published in Year Book No. 2. 



The region it is proposed to survey fortunately contains magnetic 

 observatories in requisite number and proper distribution for fur- 

 nishing the necessary corrections to the observed magnetic elements 

 to reduce them to a common epoch. Thus, continuous records of the 

 magnetic variations required for this purpose will be available from 

 the following stations : Sitka (Alaska) , Honolulu (Hawaiian Islands) , 

 Manila (Philippines), Shanghai (China), Tokio (Japan). In addi- 

 tion to these, it is possible that there may be at the time of the pro- 

 posed magnetic survey magnetic observatories in the Samoan Islands, 

 in Siberia, and in California or vicinity in position to lend effective 

 cooperation. 



Furthermore, the numerous ports and islands will furnish excel- 

 lent opportunities for controlling instrumental constants and for ob- 

 taining any additional variation data that may be needed. 



It should also be pointed out that the plan of the courses as mapped 

 permits ready adjustment for closed areas of the observed quantities 

 in accordance with the potential hypothesis, and it may even permit 

 the testing of the accuracy of this assumption, though as regards 

 the latter more can be said at the end of a j^ear's work. 



While it is not anticipated that any marked irregularities in the 

 distribution of the earth's magnetism will manifest themselves over 

 the deep waters of the Pacific, it may be confidently expected that 

 in the neighborhood of the islands and along the coasts distortions 

 and irregularities will reveal themselves. With the aid of the 

 results of the detailed magnetic survey of the United States and 

 Alaska, opportunity will therefore be afforded of studying the effect 

 of the configuration of land and water upon the distribution of the 

 19 



