PLATE 26 



10 



30" 40" 50' 



70° 80° 90° 100° 110_ 



100 110 



Tracks of Chief Vessels on Which Magnetic Observations Were Made in the Indian Ocean, 1839-1916. 



Carnegie. 1911-1916 

 Novara, 1857-1860 



Gauss, 1902-1903 Discovery. 1902-1904 



Erebus and Terror, 1839-1843 Pagoda, 1845 - 



Challenger, 1872-1876 Gazelle. 1874-1870- 



