1/2 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. JO 



the sun spots, while in Russia and Siberia it varies directly with 

 them. 



The two Lockyers call attention to the interesting circumstance 

 that at separate stations it often occurs that while the variations 

 over a long period of time follow one of the two types as at Bom- 

 bay or Cordoba for instance, they may suddenly revert for another 

 series of years to the other type, so that, for example, the air pres- 

 sure might at first vary directly as the prominences and suddenly 

 go over to the reversed type variation and after a lapse of some 

 time again go back to the original type. This is explained by the 

 Lockyers in this manner, that if a region with regular air pressure 

 variations of one or the other type experiences in a series of years 

 uncommonly great variations, the very high or very low air pressure 

 prevailing over this region must be distributed to the surrounding 

 regions of the earth and the boundary of the type of variations in 

 consequence must be displaced so that stations which lie near the 

 boundary of such a type of variation can on account of the extra- 

 ordinarily great fluctuations in neighboring regions be constrained 

 to change from one type to the other. 



These important discoveries of the two Lockyers agree as, we shall 

 see, in part with the investigations of Hildebrandsson. In the same 

 directio'n points the already mentioned observation of Hann (1904), 

 that in eighty per cent of the cases great positive air pressure 

 anomalies in Iceland corresponded with negative air pressure 

 anomalies over the Azores and that the greatest negative air pressure 

 anomalies over Iceland in eighty-seven per cent of the cases coin- 

 cided with positive air pressure anomalies over the Azores. This 

 result which was reached from the observations of the years 1846 

 to 1900 strengthens the validity of the earlier conclusion which 

 Hildebrandsson had drawn from the observational period 1874 to 

 1884 and agrees with the observations of the two Lockyers, accord- 

 ing to whom the Azores belong to the region where the air pressure 

 variations go in opposite direction to the prominences, while Ice- 

 land belongs to that region where the variations go directly with 

 the prominences. 



The result at which Prof. Bigelow arrived by his investigations 

 agrees also in general with the observations of the two Lockyers. 

 In his investigation of the year 1898, Bigelow found an agreement 

 between the variations of air pressure in the United States and 

 the variations in the sun spots and also in those of the magnetic 

 force in Europe. He found that in the northwesterly part of the 



