24 Land Magnetic Observations, 1911-13 



from March 1911 to February 1913, C. C. Craft to April 1911 and from February 

 1913. H. F. Johnston from March 1911 to April 1913, C. W. Hewlett from June 1912, 

 H. D. Frary to June 1912, C. R. Carroll to February 1912, and N. Meisenhelter 

 from March 1912. 



While too much credit can not be given the observers for their portion of the 

 work, those who have taken part at the office in the reduction and in the prepa- 

 ration of the results for publication should not be overlooked. Although the 

 observers themselves when returning from the field have frequently taken their 

 turn in making the final office-computations of one another's observations, the 

 chief burden has been borne by Messrs. J. A. Fleming, H. W. Fisk, J. P. Ault, 

 C. R. Duvall, J. H. MiUsaps, H. D. Harradon, R. R. Mills, and J. J. Carey, all 

 of the office personnel. Mention should also be made of the efficient services 

 rendered by the chief mechanician, J. A. Widmer, and his assistants, in the con- 

 struction and repair of instruments. 



DISTRIBUTION OF STATIONS. 



Some idea of the extent of the land work represented in the Table of Results 

 may be obtained from the synopsis given in Table 5, showing the geographical 

 distribution of the stations occupied during the three years, 1911-1913. Data 

 have been secured in every continent, as also on numerous islands in the Atlantic, 

 Indian, and Pacific Oceans, and, in cooperation with the Australasian Antarctic 

 Expedition, in the Victoria Quadrant of the Antarctic Regions. The work has 

 been chiefly in Australasia, South America, and Africa. The stations occupied 

 during the three years' work embraced in the present publication, and as shown 

 by the table total 983 (904 primary and 79 secondary), an average of about 325 

 per year. Of the primary stations, there are about 30 at which the full program, for 

 some reason, could not be carried out, the data for one element being in consequence 

 lacking. For the majority of these, however, magnetic results at secondary stations 

 were secured. Practically all of the secondary stations lack one or two of the 

 magnetic elements as they have been generally established for the investigation of 

 local disturbance or when time was insufficient for complete observations. 



Of the 78 C. I. W. secular-variation stations, i. e., stations where data have 

 been obtained previously by the Department of Terrestrial Magnetism, 55 have 

 been exact reoccupations, 11 have been close reoccupations (within less than 30 

 meters), 8 have been practical reoccupations (within less than 300 meters), and 4 

 proximate reoccupations (within less than 5 kilometers). It has been possible also 

 to reoccupy approximately during 1911 to 1913 more than 100 points at which 

 the magnetic elements had been observed previously by other organizations or 

 observers; about half of these are reoccupations within 300 meters and the others 

 within 5 kilometers. Thus from about 18 per cent of the stations occupied during 

 1911-1913 secular-variation and correlation data have been obtained. Twenty- 

 one of the stations have been at magnetic observatories; several of these have been 

 occupied more than once, thus affording desired data regarding the question as 

 to the degree of accuracy within which the instrumental constants can be main- 



