The _Department of Terrestrial Magnetism_ of the Carnegie Institute of Washington is engaged in continual magnetic surveys of the earth by land and sea that are of the highest value not only to navigators but also to scientists interested in solving the great and mysterious problem of the underlying causes of the earth's magnetism. To give an idea of the extent and scope of the work of this department it may be mentioned that its non-magnetic ship _Carnegie_ made in the period 1909-1918 a total run of 189,176 nautical miles, nearly nine times the earth's circumference, with an average day's run of 119 nautical miles. Magnetic observations were made practically every day at a distance of 100 to 150 miles apart. In this nine-year period five cruises were made. On her first cruise the _Carnegie_ sailed from St. John's, Newfoundland, to Falmouth, England, over practically the same course followed by the famous astronomer, Halley, in the _Paramour Pink_ two centuries earlier to determine the variation of the compass. In her fourth voyage the _Carnegie_ circumnavigated the world in sub-antarctic regions in 118 days--a record time. She has traversed all oceans from 80° North to the parallel of 60° South and has crossed and recrossed her own path and the path of her predecessor, the _Galilee_, many times, thus making it possible to determine for the points of intersection the secular changes in the magnetic elements. After a thorough overhauling in 1919 and the installation of a four-cylinder gasoline engine, _made of bronze_ throughout, to take the place of the producer-gas engine used on earlier cruises, the _Carnegie_ started on her sixth cruise with a crew of twenty-three officers and men on October 9, 1919. A cruise of 61,500 miles was planned in the South Atlantic, Indian and Pacific Oceans to last approximately two years. Unsurveyed regions in the South Atlantic and Indian Ocean were to be covered and the route was planned so as to obtain a large number of observations of the progressive changes that have taken place in the magnetic elements. This is accomplished as stated above by intersecting former routes and obtaining new values of the element at the points of intersection.