16 abstracts: terrestrial magnetism 



considerable. The usual theory of the Gerdien apparatus neglects the 

 effect of the charge collected by the rod which supports the central 

 cylinder. Experiments were made to measure directly this charge, 

 and it' was found to be far from neghgible in comparison with that 

 collected by the central cylinder. In the use of the Gerdien apparatus 

 it is important that the charging potential shall always be sufficiently 

 low. The most sensitive region of the electroscope supplied with the 

 mstruments is usually in the neighborhood of 150 to 200 volts. It 

 has been found, however, that the maximum allowable voltage varies 

 considerably from day to day, presumably owing to variations in the 

 specific ionic velocities. Usually a charging potential of 150 volts is 

 far too high. 



C. W. H. 



TERRESTRIAL MAGNETISM.— r/i.e local magnetic constant and its 

 variatioris. L. A. Bauer. Terr. Mag., 19: 113-125. 1914. 



Good progress has been made by various investigators in estab- 

 lishing the relationship between fluctuations of the Earth's magnetism 

 and those of the Sun's activity during the Sun-spot cycle. The mag- 

 netic quantity most frequently 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 interpreta- 

 tion. The result of chief interest obtained from the 1909 investiga- 

 tion was that an increase in solar activity was accompanied, in gen- 

 eral, during 1906 to 1909, by a decrease in the local magnetic constant. 

 Since this investigation, Abbot's extensive observations at Mt. Wilson, 

 California, and Bassour, Algiers, showing the fluctuations in the values 

 of the solar constant of radiation for various years, have become avail- 

 able. The question arises whether any changes in the Earth's mag- 

 netism follow the same course as that of the solar constant. 



As a provisional result, subject to modification when the final com- 

 putations have been made, it was found that for a change of 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 constant. The effect appears to be most pronounced 



