426 



Reports on Special Researches 



Figure 32 shows the corrections of the various magnetic-declination charts for the 

 portions of the Indian Ocean at the time of the Carnegie's circumnavigation cruise (No. II), 

 1911-1912. It is seen that here the corrections are larger than for Figures 29-31, reaching 

 4° to 6° at times. 



3000 



Mauritius 



NauUcal muw 

 Colomfo 



9000 



Baty 



.•ula 



•I 



♦1" 



-1 



9000 12000 Nautical mllej 1500O 16OOO 



Fig. 32. — Showing Corrections of Magnetic-Declination Charts for the Indian Ocean, 1911-1912. 



(British Admiralty, ; United States Hydrographic Office, ; German Admiralty, .) 



Figure 33 shows the corrections of the various magnetic-declination charts revealed on 

 the sub-Antarctic voyage of the Carnegie, during which she sailed from Lyttelton, New Zea- 

 land, on December 6, 1915, and returned to the same port on April 1, 1916 (see pp. 326-330). 

 The omitted portions of the curves apply to the region beyond the limits of the usual 

 magnetic charts. The magnitude of the corrections (5° to 16°) and the rapid change in 

 sign are strikingly exhibited by the curves. The large corrections apply especially to the 

 portion of the Indian Ocean, off the southwest coast of AustraUa, where the value of the 

 magnetic-declination changes very rapidly. The fact that the largest corrections in the 

 South Indian Ocean (see Fig. 33) are shown by the German Admiralty chart is fully 

 explained by the circumstance that this particular chart was issued before the Carnegie's 

 observations in the Indian Ocean during 1911 were available. 



