256 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 70 



the North Atlantic Ocean and the variations in the solar activity. 



When we investigate the relation between solar activity and ter- 

 restrial phenomena we fall upon the difficulty that we have no cer- 

 tain indicator of the variations of the solar activity. It we compare 

 the variations in the number of the prominences and in the mag- 

 netic elements of different kinds we find that the fluctuations of 

 these phenomena coincidentally are not in agreement. Their curves 

 follow somewhat different forms and we do not know which of them 

 gives the most correct expression of the variations in the solar 

 activity. More precisely expressed, we do not know which of them 

 best represents that form of solar activity which has the greatest 

 influence on the variations o'f our terrestrial phenomena. On this 

 account we are even compelled to work somewhat in the dark until 

 a greater clearness in these relations is brought about.^ 



Our curves for the air pressure difference, for the temperature, 

 etc., show, as we have already said, that it is particularly the 



^ Krogness assumes that " the magnetic storminess " is a better expression 

 of the variations of the solar activity than the sun spot numbers. If one, 

 however, compares the magnetic observations for different parts of the earth 

 he finds often a considerable disagreement. We find, for example, that the 

 fluctuations in the daily variation of declination is often very unequal in 

 Christiania, Prague, and Milan (see Wolfer Astronom. Mitt. No. C. for 1908). 

 Also we find that the curves of the disturbance of the three magnetic elements 

 in Potsdam differ very strongly from the curve of disturbance of daily varia- 

 tions of declination in Christiania. If these magnetic variations were a true 

 index of the fluctuations in solar activity there must have been a greater simi- 

 larity between them. Terrestrial conditions and partly purely local condi- 

 tions obviously play so great part in the magnetc disturbances that the solar 

 variations are more or less obscured by them, and it is difficult, or even im- 

 possible with our present knowledge, to form a satisfactory analysis of them. 

 It is, however, probable that the magnetic perturbations within the zone of 

 the Northern Lights is a fairly representative expression of the corresponding 

 variations of the solar activity, at least a much better one than the perturba- 

 tions which occur at lower latitudes where the effects are so much smaller. 

 But within the zone of the Northern Lights we have no magnetic observational 

 material that extends over a sufficient number of years to base upon it a 

 study of the long period variations. The observations best adapted for our 

 purpose have been carried on since 1843 at the observatory at Christiania, and 

 relate to the average daily variations of magnetic declination. Prof. H. Geel- 

 muyden has been of the greatest service to us, for he has with his own hands 

 made an abstract of these observations for our disposal. In table 19-M will 

 6e found the monthly anomalies computed by us for the time since i860. It 

 is fortunate that now so good an observing station as that of the Haldde 

 Observatory (Finnmark) has been erected within the circle of the Northern 

 Lights, but thus far it has not been in existence long enough for its measure- 

 ments to be used as the basis of a study of long period fluctuations. 



