468 



Sir K Lockyer and Dr. W. J. S. Lockyer. [Apr. 13, 



Thus as long ago as 1879 Blanford,* from a discussion of the 

 secular variations of barometric pressure over the wide area covering 

 Siberia, Indo-Malaysia and Australia, pointed out that there existed a 

 kind of long-period see-saw of a character that, while the pressure at 

 the tropical stations was low, that in Siberia was high, and vice versa. 

 This fact, it will be seen, is quite in harmony with the pressure-type 

 distribution, as shown in the accompanying map (fig. 1). 



Hildebrandssonf has discussed the relation between the pressure 

 variations of numerous places mainly situated in the chief centres of 

 action of the atmosphere widely distributed on the earth's surface for 

 the period 1874 — 1884. In this valuable communication, some of the 

 chief results which he was led to deduce were that there were several 

 regions which exhibited opposite types of pressure variations. 



The following places are those to which he calls attention, and for 

 comparison we give the types in brackets which have been allotted 

 according to the method adopted in the present paper ; where no type 

 is added the region has not been examined : — 



The Azores ( - ?) and Iceland ( + 11); Siberia ( - ?) and Alaska ( + ?), 

 especially in winter ; Tahiti ( ± 1) and Tierra del Fuego ; India ( + ) 

 and Siberia ( - f) ; Greenland ( + ?) and Key West (Florida) ( - ) ; 

 Buenos- Ayres (-1) and Sydney (Australia) ( + ). 



It is interesting to note that these results agree well in the main 

 with the present distribution of the regions which have been examined. 



Again HannJ has recently drawn attention to the fact that there 

 exists a see-saw between the Azores and Iceland, and he showed that 

 in 80 per cent, of cases the largest positive pressure variations at 

 Stykkisholm (Iceland), corresponded to negative pressure variations 

 at Ponta Delgada (Azores), and that the largest negative pressure 

 variations at Stykkisholm were in 87 per cent, of cases positive varia- 

 tions at Ponta Delgada. 



This result obtained from the observations extending from 1846 — 

 1900 endorses Hildebrandsson's previous conclusion deduced from 

 observations over the period 1874 — 1884, and confirms the position of 

 the neutral line shown on fig. 1, dividing the two large types of 

 pressure areas. 



Quite recently Professor Bigelow§ has published a map of the world 

 on which he has indicated the distribution of the pressure types 

 according as they follow the Indian (or direct type, as he calls it) or 

 the Cordoba (indirect) pressure variations. 



Professor Bigelow has also found that there are many regions in 



* ' Report of the Meteorology of India in 1878/ pp. 2—35. 



f " Q.uelques Recherches sur les Centres d' Action de 1' Atmosphere," 1 Kongl. 

 Svenska Velenskaps-Akad. Handlingar,' vol. 29, iso. 3. 



X ' Kaiserliche Akademie der Wiss. in Wien,' January 7, 1904. 

 § ' Monthly Weather Review,' p. 509, November, 1903. 



