Expeditions and Observatories


Interior of atmospheric-electric house on board the Carnegie, ca. 1909, Image No. C3576.

The primary mission of the Department of Terrestrial Magnetism upon its founding was to map out and, if possible, explain the earth’s magnetic field and its temporal variations.  To accomplish this mission, DTM outfitted and funded multiple geomagnetic expeditions both on land and sea. DTM director, Louis Agricola Bauer, contracted the Galilee, a brigantine built in 1891, and saw to the removal of as much iron as possible to lower the magnetic constants during voyages.  The Galilee made three voyages beginning in 1905 before a new ship, the Carnegie, was specially constructed for the department.  The Carnegie made seven voyages from 1909 to 1929 before it exploded and sank during a refueling in Apia, Samoa. 

Testing a resistivity meter for the field in Maryland in 1925, Image No. I889.

Bauer arranged extensive land expeditions, and his observers covered every continent and the Caribbean and Pacific islands beginning in February 1905.  Bauer collaborated with magnetic institutions already in place around the world, and thus he focused DTM’s work on those locations where magnetic observations were most needed and there were no local institutions to do the job.  The expeditions generated massive amounts of data on the earth’s magnetic field through the department’s extensive land efforts.  In the first ten years of the mission, observers established approximately 2500 magnetic stations in 94 countries or colonies around the world, leading Bauer to estimate that DTM’s World Magnetic Survey was already two-thirds completed.

Theodolite-magnetometer shown in its packing case for travel, 1909, Image No. I209.
Improved DTM observing tent and canopy, 1931, Image No. I2240.


To make their observations, the expedition parties brought magnetometers, dip circles, and earth inductors with them as well as chronometers, watches, non-magnetic observing tent, and other accessories.  The instruments and some of the field equipment taken on the ships and on land expeditions were carefully photographed and added to the instrument photo albums as they were acquired, used, and modified by DTM.  The department had its own instrument shop, and the chief mechanician, J. A. Widmer, placed priority on increasing the precision and accuracy and decreasing the weight of the instruments that were to be taken into the field.   Portability was crucial for the land instruments, and the photographs often include images of the wooden cases in which the instruments were disassembled and carefully housed.  Observers were held responsible for their equipment, which was packed in pieces in special wooden cases that were specially constructed at DTM to protect the instruments in harsh field environments.  


Ionospheric installation at Watheroo Magnetic Observatory showing oscillograph, tube rack, and spares in December 1938, Image No. DTM 16281.

Although the cruises and expeditions of the World Magnetic Survey generated extensive data, DTM needed permanent observatories to expand on knowledge of the temporal variations as well as diurnal and secular variations of the earth’s field and to provide information about magnetic storms.  The presence of multiple observatories around the world would further allow for simultaneous recordings of temporal changes.  In 1915, DTM selected two locations for new observatories in the southern hemisphere, where more observatories were particularly needed. The Watheroo Magnetic Observatory opened in southwestern Australia in 1919, and the Huancayo Geomagnetic Observatory in the Peruvian Andes opened in 1922.  The Carnegie Institution operated the locations until 1946, when they were transferred to the Australian and Peruvian governments.

Special switchboard intended for installation at Watheroo Observatory in 1924, Image No. I793.

In addition to monitoring magnetic events, the observatories initially studied the variation of the electric potential and conductivity of the air, earth currents, cosmic rays, and disturbances in the Sun’s chromosphere.  They also provided meteorological information for the benefit of the local region.  DTM developed and supplied equipment for Huancayo and Watheroo for magnetic, electrical, cosmic ray, and seismic investigations, and this instrumentation is featured heavily in the photograph collection.  In the 1930s, the observatories installed the large multifrequency sounding equipment that DTM scientist Lloyd Berkner had developed to record the height of the ionosphere.  The photograph collection also contains rare images of smaller field stations set up by DTM around the world for geomagnetic and ionospheric observations.