ILLUSTRATIONS. 



Plate 1. Headquarters and Laboratorj- of Department of Terrestrial Magnetism, Washington, D. C Frontispiece 



OPPOSITE 

 PAGE 



Plate 2. 1, 2, 3, Combined Magnetometer and Dip Circle. [Universal Magnetometer of Type 4 (fe) .] 4, Dividing 



Engine for Graduation of Instrument Circles 4 



PL.4TE 3. Combined Magnetometer and Earth Inductor. [Universal Magnetometer of Type 4 (e).] 10 



1, Attachments and Appurtenances. 2, Instrument packed in its Case. 3, General View of Galvanom- 

 eter. 4, Interior View of Galvanometer. 



Plate 4. Earth Inductors and Galvanometer 16 



1, Type 4 (c) for use on Land. 2, Type (6) for use on Land and Sea. 3, Type (h) for use on Land. 

 4, Galvanometer used with Type (6) for Land Work. 



Pi.ATE j. Typical Views of Magnetic Expeditions in North and South America 24 



I, Osnaburgh House, Hudson's Bay Post, Canada. 2, Fawcett's Post, Lake St. .loseph, Canada. 

 i. Fort Albany, Hudson Bay. 4, Kurupukarri Falls, British Guiana. .5, Huarnonia, Bolivia. 

 6, Monterideo, Uruguay. 



Plate fi. Typical Views of Magnetic Expeditions in Europe and Africa 64 



1, Near Obser\-atorj', Cape Town. 2, Valctta, Malta. 3, Near Fort Motylinski, Algerian Sahara. 



4, Comparison stations at Terracina, Italy. 5, Tripoli, TripoUtania. 



Pii^TE 7. Typical Views of Magnetic Expeditions in Asia and Australia 128 



1, Lao-Kay, Tonldn, Indo-China. 2, Pitsanuloke, Siam. 3, Oodnadatta, South Australia. 4, Oatlands, 

 Tasmania. 5, Dehra Dun; Base Station of Magnetic Suri'ey of India. 6, .\libag Magnetic Observa- 

 tory, India; House for Absolute Observations. 



Pl.\te 8. Research Buildings of Department of Terrestrial Magnetism 184 



1, General View of Main Building (Headquarters and Laboratory) and of Grounds. 2, Detail View of 

 Front Entrance to Main Building. 3, Standardizing Magnetic Observatory. 



Plate 9. Interior Views of Main Building (Headquarters and Laboratory) 192 



1, Library and Lecture Room. 2, East Laboratory Room. 3, General Instrument Shop. 4, Switch- 

 board. 



Plate 10. Echpse Expedition to Manua, Samoan Islands, April 28, 1911 206 



1, General View of Eclipse Station at Tau, Manua Island. 2, Path of TotaUty for Solar Eclipse, April 28, 

 1911. 3, The Solar Corona as Photographed at Tau, Manua Island, April 28, 1911. 4, Professor 

 Langley's Sketch of the Solar Corona, 1878. 5, Capt.ain Holford's Sketch of the Solar Corona, 

 April 28, 1911. 



Plate 11. Views of Magnetic Observatories in Asia, Mauritius, Java, and Philippines 222 



1, Zi-ka-wei, China. 2, Kodaikanal, India. 3, Bata\ia, Java. 4, Antipolo, near Manila, Philippines. 



5, Royal Alfred Observatory on Mauritius Island. 6, Colaba, near Bombay, India. 



Plate 12. Views of Magnetic Obser%'atories in Europe, Russia, and Egypt 250 



1, Seddin, near Potsdam, Germany. 2, Kew, England. 3, Rude Skov, near Copenhagen, Denmark. 

 4, Falmouth, England. 5, Helwan, near Cairo, Egypt. 6, Tiflis, Transcaucasia. 



Pl-vte 13. Views of Magnetic Observatories in North and South America 268 



1, Pilar, near Cordoba, Argentina. 2, Ottawa, Canada. 3, Vassouras, near Rio de Janeiro, Brazil. 

 4, Department of Terrestrial Magnetism, Washington, D. C. 5, Vieques, Porto Rico. 6, Chelten- 

 ham, Maryland. 



TEXT-FIGURES. 



PAGE 



Fig. 1. Plan of Grounds and Contour Lines. A, Main Building. B, Standardizing Magnetic Observatory. C, Acces- 

 sory Buildings 187 



Fig. 2. Details of Front Entrance to Main Building 189 



Fig. 3. Transverse Section and Elevation of Main Building 190 



Fig. 4. Plan of Sub-basement of Main Building 193 



Fig. 5. Plan of Basement of Main Building 194 



Fig. 6. Plan of First Floor of Main Building 196 



Fig. 7. Plan of Second Floor of Main Building 197 



Fio. 8. Plan of Attic and Roof of Main Building 198 



Fig. 9. Plan and Details of Standardizing Magnetic Observatory opposite 198 



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