DEPARTMENT OF TERRESTRIAL MAGNETISM. 20I 



instrumental and to theoretical matters. Besides the usual repair work in the 

 shop, two new types of magnetometers, one of which is of a very portable 

 character designed for difficult land expedition and capable of measuring all 

 the magnetic elements, have been constructed. An improved form of our 

 "deflector" has also been made for measuring declination and horizontal in- 

 tensity at sea. I must express my obligation to Mr. Fleming for the efficiency 

 here obtained. During my absence in the field he was placed in sole charge 

 of the office work. He refers to the effective assistance received from vari- 

 ous members of the office staff. 



The President, in his report for 1910, speaks of the "utilitarian results," 

 besides the benefits to science, which "may come from a deeper knowledge 

 of the earth's magnetism and its cosmic connections." The utilitarian results 

 to navigation at present accruing from the revealed chart errors are immedi- 

 ately recognized. Some mariners, to be sure, at first thought our work "ultra- 

 scientific," but it was soon found that our observations disclosed errors in 

 the charts frequently exceeding considerably their assumed accuracy of the 

 "lines of equal magnetic variation," 



To reap full advantage of the observational work now in progress, it 

 has been found advisable to undertake immediately various preliminary in- 

 vestigations pertaining to the theory of the earth's magnetism and of its 

 variations. These theoretical researches, of which four have been completed 

 thus far, and a fifth is in progress, are being published in the journal 

 "Terrestrial Magnetism and Atmospheric Electricity," the form chosen being 

 such as to give other magneticians an opportunity to participate in helpful 

 discussions of more or less mooted questions of theory. Several lines of 

 inquiry have been revealed, along which further research might be profitably 

 conducted. An impetus has been given for stimulating interest in securing 

 greater accuracy than has been generally attained hitherto in the time-scalings 

 of important events recorded on magnetograms. Various magneticians are, 

 in consequence, at present engaged in a renewed study of the magnetic 

 perturbations, especially with reference to the question as to whether even 

 the most sudden of these phenomena occur at the same measurable instant 

 of time all over the globe. 



DETAILS OF MAGNETIC WORK, NOVEMBER 1, 1910, TO OCTOBER 31, 1911. 



LAND WORK, 



Africa. — Upon the completion of his work in Turkey and Arabia, Magnetic 

 Observer W. H. Sligh made magnetic observations along the shore of the 

 Red Sea at four stations, occupied the secular variation station at Suez, and 

 carried out intercomparison observations at Helwan Magnetic Observatory, 

 Magnetic Observer H. F. Johnston, en route to join the Carnegie at Cape 

 Town, observed the magnetic elements at the secular variation station at 

 Free Town, Sierra Leone, and at two stations in the Canary group. 



