196 aNjNual eefoet Smithsonian institution, 1913. 



According to the regulations governing this lecture, it is to be 

 known as the "Halley lecture on astronomy and terrestrial mag- 

 netism." "Astronomy shall include astrophysics, and terrestrial 

 magnetism shall include the physics of the external and internal 

 parts of the terrestrial globe." This lecture might, therefore, with 

 ]:)ropriety cover the whole range of investigation in terrestrial and 

 cosmical magnetism. However, we must limit ourselves to those 

 particular lines of research in our subject in which Halley himself 

 was chiejfly interested. It so happens that these are the very lines 

 also in which I have been given the opportunity to continue and 

 expand the work begun by him. 



After Halley had made two attempts to establish a working 

 theory respecting the distribution of terrestrial magnetism and the 

 cause of its striking change with the lapse of years — the so-called 

 secular variation — he must have reached the conclusion that the 

 elusive problem of the earth's magnetism would be more profitably 

 advanced by additional facts than by further speculation. That, 

 paraphrasing Seneca, to avoid making a false calculation of matters, 

 it were better to advise with nature rather than with opinion. Ac- 

 cordingly we find him setting out in October, 1698, in command 

 of a sailing ship, the Para/mouv Pinh, and cruising in her under 

 orders from the British Government, back and forth, north and south, 

 in the Atlantic Ocean for two years, observing almost daih^, some- 

 times several times in a day, the angle which the compass needle 

 makes with the true north and south line — the angle known to the 

 man of science as the magnetic declination, to the mariner and sur- 

 veyor as the " variation of the compass." 



This is memorable as being the first scientific expedition sent out 

 by any country with the specific object of improving existing knowl- 

 edge regarding certain facts of the earth's magnetism. Not until 

 somewhat over two centuries later did it occur again, that a sail- 

 ing ship traversed the oceans with the chief purpose of making 

 magnetic observations.^ In July, 1905, there sailed from the port of 

 San Francisco, Cal., a chartered sailing yacht, the Galilee^ sent 

 under the auspices of the Carnegie Institution of Washington, on 

 the sole mission to determine the magnetic elements at sea, for 

 the benefit of both the mariner and the man of science, as was also 

 the purpose of Halley 's voyages. Four years later, in 1909, a 

 specially built nonmagnetic vessel, likewise under the auspices of 

 the Carnegie Institution of Washington, left New York for St. Johns, 

 Newfoundland, and thence proceeded to Falmouth, along practically 



' Valuable magnetic data have been secured by various expeditions since Halley's time, 

 but either the magnetic work was merely incidental or formed part of a general scientific 

 ))rogram, or was combined with some geographical object such as Arctic or Antarctic 

 I'xploration — (be memorable Erebufi and Terror expeditions, for example. 



