248 ANNUAL EEPORT SMITHSONIAN INSTITUTION, 1925 



field instruments the Department of Terrestrial JNIagnetism has been 

 particularly active, to meet the A'cry varied conditions under which it 

 has had to operate, especiall}- in the matter of observations at sea. 

 The design of a portable galvanometer, for use Avith the earth induc- 

 tor, has made it possible to use that instrument in the field in place of 

 the dip circle, and the addition of a special device for rotating the 

 coil of the earth inductor adapted it for use on board ship. The 

 marine collimator permits more accurate declination observations at 

 sea, and the sea deflector provides a method of determining directly 

 the horizontal intensity on board ship. INIagnetometers have been 

 improved to secui'e greater ease of handling, adjustment and trans- 

 portation, and various combination instruments have been devised 

 for use where a very light, compact outfit is essential. 



The sine galvanometer, of which three types have been developed, 

 provides an electrical method for determining the horizontal inten- 

 sity, combining rapidity with great accuracy. It is particularly well 

 adapted for a standard instrument, and in Japan it has been used 

 successfully in the field. 



The variometers designed by Eschenhagen, with very small mag- 

 nets, have permitted the erection of smaller observator buildings 

 for the variation instruments and a decrease in the cost of operation, 

 since it is possible to have tliree vai'iometers record on a single pho- 

 tographic sheet. More complete control of the instrumental con- 

 stants is also provided. 



With so much energy being devoted to the collection of observa- 

 tional data, it would not be surprising to find a falling off in the 

 attention paid to the discussion of results; but this has been true 

 only to the extent that the utilization of the data has not kept pace 

 Avitli its accumulation. There has been no falling off in the zeal with 

 which magneticians have attacked the problems awaiting solution. 

 JNIany of those who had taken a prominent part in the investigations 

 of the last half of the nineteenth century have gone one by one, 

 leaving their places to be filled by a younger generation. Schott, 

 Eschenhagen, Wild, von Bezold, Snellen, Borgen, Sutherland, 

 Fritsche, Bidlingmaier, Neumayer, Riicker, Birkeland, and Leyst 

 are among tliose whose names will always be recalled when review- 

 ing the progress during that period. 



The fundamental problem of the cause of the earth's magnetism 

 and its variations, attacked from many sides and with various 

 weapons, has thus far withstood the attack. One theory after an- 

 other has been advanced only to be withdraAvn before the irresistible 

 assault of observed facts. Some theories fitted well enough quali- 

 tatively, but we4e entirely inadequate when quantity was taken into 



