DEPARTMENT OF TERRESTRIAL MAGNETISM. 323 



with which all the magnetic elements may be measured by electrical methods 

 are at present under consideration, but not yet definitely decided upon. 



Summing up, it appears theoretically possible to construct an apparatus 

 for measuring, by electrical means, the intensity of the Earth's magnetic field 

 more expeditiously and, in general, with greater accuracy than with present 

 magnetic methods, provided the necessary precautions be taken. Considerable 

 experimentation appears yet to be required before it will be entirely advan- 

 tageous to replace the present magnetic methods wholly by electrical ones. 



The local magnetic constant and its variations. L. A. Bauer. Terr. Mag., vol. 19, pp. 

 113-125 (1914). 



Good progress has been made by various investigators in establishing the 

 relationship between fluctuations of the Earth's magnetism and those of the 

 Sun's activity during the sun-spot cycle. The magnetic quantity most fre- 

 quently used for this purpose has been the range of the diurnal variation — 

 generally of the magnetic declination. In connection with a preliminary 

 examination of this relationship, made in 1909, occasion was found to employ 

 various other magnetic quantities. One of these was what is here termed the 

 "local magnetic constant," which, under certain assumptions, is proportional 

 to the magnetic moment of the Earth, or to the intensity of magnetization; it 

 is thus a quantity which lends itself readily to physical interpretation. 



The result of chief interest obtained from the 1909 investigation was that 

 an increase in solar activity was accompanied, in general, during 1906 to 1909, 

 by a decrease in the local magnetic constant. Since this investigation, Abbot's 

 extensive observations, at Mount Wilson, California, and Bassour, Algiers, 

 showing the fluctuations in the values of the solar constant of radiation for 

 various years, have become available. The question arises whether any 

 changes in the Earth's magnetism follow the same course as that of the solar 

 constant. 



In order to eliminate, as far as possible, the effects attributable perhaps to 

 phenomena associated with sun-spots, the years chosen for the first tests were 

 1911 and 1912, the latter being the year of sun-spot minimum according to 

 Wolfer's numbers. The magnetic data used for comparison with the Mount 

 Wilson solar-constant values were those at the nearest magnetic observatory, 

 namely, that of the United States Coast and Geodetic Survey at Tucson, 

 Arizona, in longitude 29 minutes of ti me east o f Mount Wilson. Accordingly, 



the local magnetic constant, G = \\H^-\--r-Z'^, was obtained for each day on 



which there were solar-constant values of the grade good and above, H being 

 the horizontal intensity and Z the vertical intensity. The time for which G 

 applied was the same as for the solar-constant values. Next was tested the 

 series of magnetic observations at Pola, on the Adriatic, the nearest observa- 

 tory to Bassour, Algeria, via Pola, being in longitude 44 minutes of time east 

 of Bassour. 



As a provisional result, subject to modification when the final computations 

 have been made, it was found that for the maximum change (10 per cent) 

 observed in the solar-constant values, there is apparently a change in the local 

 magnetic constant of about 0.03 per cent of its value, i. e., about 10X10"^ 

 C G. S., decreased magnetic constant corresponding to increased solar con- 

 stant. This result, if correct, is extremely interesting, not only because of its 

 magnitude, but especially as it would be similar to that caused by heating a 

 magnet, though it is not to be inferred at present that the effect is of this 

 nature. The effect appears to be most pronounced for the observatories in 

 the sun-lit portion of the globe, and seems to be reversed for the observatories 



