ILLUSTRATIONS. 



Plate 1. Typical Views of Magnetic Expeditions in Asia Frontispiece 



1, Ongin River, Mongolia. 2, Gorges of the Yangtze River, China. 3, Mongol village, Mon- 

 golia. 4, Caravan, Yiinnanfu, China. 5, Sungtao, China. 6, Near Hengchowfu, China. 

 7, Meitan, China. 8, Tibetan border, Siningfu, China. 



OPPOSITE 

 PAGE 



Plate 2. Magnetic Instruments for Amundsen Arctic Expedition ("Maud Expedition") 8 



1, Theodolite of magnetometer. 2, Magnetometer on tripod. 3, Dip circle, showing also 

 special tripod-clamps. 4, Dip circle and appurtenances. 



Plate 3. Typical Views of Magnetic Expeditions in Africa 98 



1, Transportation, Cameroun. 2, Huambo, Angola. 3, Mangal, Cameroun. 4, Hanging 

 bridge, French Equatorial Africa. 5, Eseka, Cameroun. 6, Waldea, Abyssinia. 



Plate 4. Typical Views of Magnetic Expeditions in Australia 130 



1, Camp, Wiluna, Western Australia. 2, Landing, Roper River Mission Station, Northern Ter- 

 ritory. 3, C. I. W. caravan, Eucolo Creek, South Australia. 4, Boundary rider's hut, 

 rabbit-proof fence, Western Australia. 5, Kunningarra Range near No. 48 Well (typical 

 hills of interior), Western Australia. 6, Magnetic Island near Townsville, Queensland. 



Plate 5. Typical Views of Magnetic Expeditions in North and South America 164 



1, San Mateo, Peru. 2, Woodland Park, Colorado, United States. 3, Trachyte Mt., Colorado, 

 United States. 4, Quixada, Brazil, showing huge outcroppings of granite. 5, Andes near 

 Puente del Inca, Argentina. 6, Chupaca River, Peru. 7, Ashe Inlet, Northwestern Terri- 

 tories, Canada. 8, Bocas del Toro, Panama. 



Plate 6. Typical Views of Magnetic Expeditions in South America 194 



1, View on road to Bogota, Colombia. 2, Andes village, Colombia. 3, Punta Arenas, Chile. 

 4, Maraba, Brazil. 5, Llama pack-train near Tirapata, Peru. 6, Transportation, Punta 

 Arenas to Ultima Esperanza, Chile. 



Plate 7. Typical Views of Magnetic Expeditions in Islands of the Atlantic and Pacific Oceans 222 



1, Walpole Island, Pacific Ocean. 2, Guam Island, Pacific Ocean. 3, Edwards Point, South 

 Georgia Island, Atlantic Ocean. 4, Teneriffe Island, Atlantic Ocean. 5, Makambo Island, 

 Pacific Ocean. 



Plate 8. Non-Magnetic Experiment Building of the Department of Terrestrial Magnetism 350 



1, View from southwest. 2, Interior view. 



Plate 9. Sine Galvanometer 374 



A and B, Views of the new instrument. C, Magnetometer box, upports for box and spool, and 

 device to insure correct turning and orientation. D, Spool, complete with coils, in machine 

 for measuring diameters. 



TEXT-FIGURES. 



PAGE 



Effect of Change of One Minute of Arc in Latitude on Azimuth of Mark or on Correction on Local 



Moan Time 27 



Plan of Grounds of Department of Terrestrial Magnetism, Washington, D. C. A, Main labora- 

 tory. B, Standardizing Magnetic Observatory. C and D, Accessory buildings. E, Ex- 

 periment Building. F, Foundry, storehouse, and stable 352 



Plan, End Elevation, Cross-Section, and Detail Section of Non-Magnetic Experiment Building. 355 



Correction-Curves for Needles used with Circle No. 177 during March to July 1915 361 



Correction-Curves for Needles used with Circle No. 41 during 1914 363 



Correction-Curves for Needles used with Circle No. 177 during August 1915 to July 1916 364 



Showing Time-Change in Correction-Curve for Needle No. 1 of Circle No. 177 366 



and 86. Theory of Minute Pivot-Defects on Dip-Needle Axles 367 



and 96. Theory of Minute Pivot-Defects on Dip-Needle Axles 368 



Observed and Computed Correction-Curves for Needle No. 5 of Circle No. 177 370 



Magnet^Mirror Holder 376 



Horizontal Section of Spool 378 



Horizontal Section of Mandrel u-ed in Precise Turning of Spool 379 



Horizontal Section of One Pair of Terminals 380 



Diameters of the Spirals 385 



Axial Distance- between Co-responding Turns of the Spirals 386 



Angles involved in the Theory of the Sine Galvanometer 390 



VI 



