224 



SCIENCE. 



IN. S. Vol. XV. No. 371. 



ing details in the results from the different 

 stations, merely noting that the vectors for 

 the diurnal variation at Fort Rae move in a 

 direction opposite to that at all other stations. 



The study of the course of the magnetic 

 variation throughout the year makes it appear 

 that all phenomena occurring in any one sea- 

 son in the southern hemisphere do not, as was 

 formerly supposed, correspond to those of the 

 opposite season in the northern; on the con- 

 trary, certain features in the yearly variation 

 seem to indicate the presence of influences 

 outside the Earth, affecting the Earth as a 

 whole. The dependence of the variation upon 

 the latitude of the station is brought out with 

 great clearness. 



The above results have an important bear- 

 ing upon Schuster's theory of the diurnal 

 variation. This theory, as von Bezold has 

 pointed out, requires an invariahle system of 

 forces, in whose fi.eld the Earth rotates. Wein- 

 stein's deductions show that excessive de- 

 formations of the system would be needed to 

 account for some of his observed phenomena, 

 so excessive, in fact, as to lend strong evi- 

 dence in favor of local influences. We must 

 therefore assume at least two systems of 

 forces, one external, possibly subject to varia- 

 tions, the other of local character. 



This part of the work concludes with a dis- 

 cussion of secondary magnetic waves, of 

 which, for Wilhelmshafen in 1884, a mean of 

 36 were detected in the course of a day, in the 

 case both of declination and of horizontal 

 intensity. The connection between waves in 

 the two elements could not however be estab- 

 lished with certainty. It is at least significant 

 that the number of secondary waves here is 

 the same as in the case of the earth-currents. 



The work reaches its culmination in Part 

 III., where the relation between terrestrial 

 magnetism and earth-currents is discussed. We 

 regret that space does not permit a more ex- 

 tended review of this interesting chapter. To 

 test first the hypothesis that the earth-currents 

 are simply inductive currents caused by 

 changes in the Earth's magnetism, the author 

 compares the mean diurnal variation in ver- 

 tical intensity for Vienna in 1884, with that of 

 the earth-currents for the same year. Instead 



of maxima in increase of vertical intensity 

 corresponding to maximal current, etc., we find 

 almost the reverse to be the case. The author 

 therefore confines himself to the question 

 whether variations in magnetism are partly 

 due to the earth-currents. If the vertical 

 component of the cui'rent changes were known, 

 the problem would be much simplified; in lieu 

 of this, ingenious methods have to be resorted 

 to in order to gain such circumstantial evi- 

 dence as is possible. Even in a horizontal 

 direction only the mean components for cer- 

 tain distances in two directions are known, 

 while the true path of the current lies wholly 

 in the dark. An increase in one or both of 

 these components would not of necessity cause 

 an increase in any one of the magnetic ele- 

 ments, since any such effect might be more 

 than counterbalanced by changes in the direc- 

 tion of the earth-current. 



A comparison of the mean absolute values 

 of vertical magnetic intensity and earth-cur- 

 rent intensity for the 24 hours tends to 

 strengthen the theory. To explain certain 

 peculiarities in the former, assumptions are 

 made concerning the variation in direction of 

 flow of the earth-currents, which in turn 

 would require an increase in the magnetic 

 horizontal intensity; and this increase is in 

 fact found to take place. When the changes 

 in azimuth of the horizontal components of 

 earth-current and magnetic intensity are com- 

 pared, the evidence is weaker, though still in 

 the sarae direction. The comparison of 

 changes from season to season is also favor- 

 able, certain minor variations agreeing re- 

 markably well. 



As concluding evidence, reference is made 

 to the parallelism in the occurrence of sud- 

 den disturbances. By picking these out on 

 the declination traces in Vienna and com- 

 paring them with corresponding disturbances 

 on the Berlin earth-current records, the dif- 

 ference in longitude between the two cities 

 could be quite accurately determined. A 

 rigid comparison would of course be possible 

 only if both direction and amount of the re- 

 sultant disturbances were known, which is far 

 from being the case in the present state of the 

 science. 



