TERRESTRIAL MAGNETISM HAZARD , 247 



covering; practically tlie whole surface of the earth between latitude 

 70° north and 60° south. 



At the same time the making of magnetic observations has been 

 recognized as an important part of the work of an exploring expe- 

 dition, and as a result much information has been obtained regarding 

 conditions in regions which would not ordinarily be reached. This 

 is particularly true of the polar regions. The Ziegler expedition to 

 Teplitz Bay, in 1903 and 1904, Amundsen's work in the vicinity of the 

 magnetic North Pole, 1903-1906, and along the north coast of Siberia 

 in 1918-1921, and the work of MacMillan's two expeditions served 

 to reduce materially the size of the magnetically unexplored region 

 around the North Pole, while the various South Polar expeditions, 

 German, French, British, and Australasian, between 1902 and 1912, 

 supplied a large amount of valuable information regarding mag- 

 netic conditions on the borders of the Antarctic Continent, and served 

 to locate the position of the south magnetic pole within narrow 

 limits. The operation of temporary magnetic observatories by some 

 of the expeditions made possible a comparison of the magnetic varia- 

 tions in polar regions with those in lower latitudes, the value of the 

 comparison being enhanced by cooperation at a number of leading 

 observatories in the form of a more open time scale on the magneto- 

 grams at specified times. 



While there were plenty of magnetic observatories in operation 25 

 years ago, their distribution was very unsatisfactory. Out of about 

 40 making reports, 70 per cent were in Europe; there was only one 

 in North America (Toronto), none in South America, and only four 

 in the Southern Hemisphere. With the new observatories established 

 since that time there has been a great improvement in the geographi- 

 cal distribution, so that more than 50 per cent of the present active 

 observatories are outside of Europe and 10 are in the Southern 

 Hemisphere. Here again the United States has taken a leading part. 

 Observatories have been operated by the Coast and Geodetic Survey 

 at Cheltenham, Md.; Tucson, Ariz.; Vieques, P. R. ; Sitka, Alaska; 

 and near Honolulu, Hawaii, and by the Department of Terrestrial 

 Magnetism at Watheroo, Australia, and Huanca^^o, Peru. Other new 

 observatories at Cordova and Ncav Year Island, Argentina; Vas- 

 souras, Brazil ; Apia, Samoa ; Christ Church, New Zealand ; Dehra 

 Dun, India; Helwan, Egypt; Sodankyla, Finland, and Meanook, 

 Canada, have all helped to extend the area covered. At the same 

 time some of the older observatories have been discontinued, and 

 others have been compelled to move to new sites, because of the 

 encroachment of electric car lines and other industrial developments. 



Improved methods and instruments have added materially to the 

 accuracy of the results. In the development of new and imi)roved 



