214 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 70 



solar activity, and it is possible that they may be used advan- 

 tageously as a measure of it. 



In the curve M of figure 71 we have given the variations in the 

 degree of disturbance (measured as the number of unquiet hours) 

 of the three magnetic elements, the declination, horizontal-intensity 

 and vertical-intensity at Potsdam. The degree of disturbance of the 

 elements is reduced to characteristic numbers according to Eschen- 

 hagen's system. The scale is given on the right. The reader will see 

 that the curve shows maxima in the years 1892, 1894, 1903 and 1904, 

 and 1907, when the curve for the air pressure in Bombay shows 

 minima, while in the years 1890-91, 1893, 1895, and 1901, the disturb- 

 ance of the magnetic elements was small when the air pressure in 

 Bombay had either maxima or was relatively high. In the years 1897 

 and 1898-99, on the other hand, both curves showed simultaneously 

 minimum or maximum. We see from tills that the agreement 

 between the two curves is not complete whether one takes them 

 direct or inverted. 



Going on from this to compare the curve for the prominences 

 and the magnetic elements at Potsdam, with the air pressure curves 

 in the other stations in the Indo-Malayan region given on figure 71, 

 namely Batavia, Wellington, Mauritius, Antananarivo, we find the 

 same result — that the relations are sometimes direct, sometimes in- 

 verse. For example the maximum of prominences in the years 

 1884 and 1885 was found simultaneously with the maximum of air 

 pressure in Batavia and Wellington ; and also the minimum of promi- 

 nences in the years 1889-90 finds a corresponding minimum of air 

 pressure in Batavia, Wellington, Mauritius, and Antananarivo. On 

 the other hand, the maximum of prominences in the magnetic curves 

 for 1892 corresponds with the minimum of the four air pressure 

 curves. Therefore there is a variable relation, as already found, fo'r 

 the air pressure curve for Bombay. 



If we take now the air pressure variations after 1900 for Batavia 

 and compare them with the magnetic curve for Potsdam we see that 

 while, for example, the minimum of the magnetic curve for 1901 

 corresponds with a small secondary minimum in the air pressure 

 curve for Batavia, yet the maximum of the magnetic curve for 1903 

 and 1904 corresponds with the minimum in the air pressure curve 

 for Batavia. On the other hand, in the time about 1905-8, the two 

 curves run approximately parallel. In the year 1910, again the 

 maximum of the magnetic curve corresponds to the minimum of 

 the air pressure curve of Batavia, while in the year 1911 these two 



