June 23, 1904] 



NATURE 



177 



A WORLD-WIDE BAROMETRIC SEE-SAW. 



IX the year 1902, an account was given in tliis Journal 

 (vol. Ixvi. p. 248) of a short period atmospheric 

 barometric variation which appeared to be closely re- 

 lated to the changes in the percentage frequency of 

 prominences as observed year by year on the limb of 

 the sun. In a later article, which appeared in the 

 following year (vol. Ixvii. p. 224), it was shown 

 that this barometric variation consisted really of a 

 great see-saw between two nearly antipodal parts of 

 the earth, the one region about India and its neigh- 

 bourhood behaving in an inverse way to that of South 

 .America and the southern parts of the United States. 

 A further study of these pressure changes has recently 

 been communicated by Sir Norman Lockyer and the 

 writer to the Royal Society, the object being to trace 

 the behaviour of these variations in as many regions 

 of the earth's surface for which observations covering 

 a sufficient period of time are available. 



For this, so to speak, classification of pressure vari- 

 ation types, the system adopted was to take the 

 pressure variations over India and Cordoba as the chief 

 t>'pes of each region, denoting those 

 of the former by the symbol ( + ), 

 and those of the latter by ( — ). The 

 pressure curve of any other place 

 was then taken and compared with 

 each. If, for e.xample, it was found 

 that the curve extending over 

 several years exhibited an excess 

 pressure at those epochs when the 

 Indian pressure curve was in excess, 

 then it was classified as being- 

 similar to the Indian type and re- 

 presented by a ( + ). If it was seen 

 that although it was more like the 

 Indian curve than that of Cordoba, 

 but yet not quite the exact counter- 

 part of India, then it was denoted 

 bv (+ ?). In a similar way pressure 

 curves like Cordoba were classified 

 as ( — ), and those more like Cordoba 

 than India as (— ?). 



In some regions the pressure 

 variation curves were distinctly a 

 mixture of both the Indian and 

 Cordoba types, and it was difficult 

 to classify them satisfactorily by the 

 above method. The symbol adopted 

 for these cases was (+?). Again, there were further 

 some curves, but very few in number, in which even 

 this mixed type of symbol was not sufficient to exhibit 

 the relationship of their variations to the other curves, 

 so a special symbol (?) denoting ambiguity was used. 



It may here be mentioned that the pressure curves 

 liere utilised for discussion were not always formed 

 from the values obtained by plotting the annual means, 

 but from the means of the groups of consecutive 

 months in which the pressure was above or below the 

 VI arly mean value. Such a division of the year can be 

 accurately determined for places which have a regular 

 and pronounced annual pressure variation, such as 

 India, and where the yearly barometric range is of far 

 greater magnitude than any other aperiodic fluctu- 

 ation. In those regions where the mean yearly curve 

 i- more misleading than otherwise, such as the case 

 'i' the British Isles, the divisions according to the two 

 -. ;i>ons included in the two groups of months, April 

 to .September and October to March, were adopted. 



In examining the curves for the similarity or dis- 

 similarity of the pressure changes, it was found that 

 the special types were apparent sometimes in the yearly 



NO. 1808, VOL. 70] 



curves, sometimes in those for one or other of the high 

 or low pressure groups of months, or sometimes in 

 both of these. It did not, however, appear to follow 

 that, because the type was distinguishable in the yearly 

 curves, it was necessarily apparent in both the curves 

 of the high and low pressure months. 



On the accompanying map of the world are marked 

 the types of pressure variations in each region included 

 in this barometric survey. 



Although the above classification gives a very fair 

 idea on the whole of the types of pressure variations 

 from one region to another, minor peculiarities have 

 been met with which have tended to add a certain 

 amount of difficulty. These remarks apply principally 

 to places in the more northern latitudes. Thus, for 

 instance, Greenland and Iceland have been classified 

 as of the (+ ?) type, the British Isles, Germany, and 

 Spain of the (+?) type, and the Azores of the (- ?) 



type- 

 While the western portion of Europe is of the ( + ?) 

 type, the eastern portion gradually assumes the (—?) 

 type, and this region extends not only probably to 

 Norwa-y and Sweden, but right across European and 



I.— Showing the distribution of the different types of pre 



ire roUEhly separated by the neutral lines. Previously known 



hort continuous straight lines connecting the two regions marked i 



shown by the 



Asiatic Russia. The European Russian type of curve 

 has an undoubted similarity to those of more western 

 Europe, but there are variations which indicate that 

 the type is more like that of Cordoba than India. 



-Again, another region in which rather mixed types 

 of pressures are met with is that of eastern and north- 

 eastern Canada. Curiously enough. Prince Edward 

 Island and Sydney (Nova Scotia) correspond very 

 closely to the ( — ) type, if allowance be made for the 

 differences about the year 1S77. The inverted curve 

 for the latter with the Adelaide (.Australia) pressure 

 curve for comparison is shown in Fig. 2. 



In addition to illustrating this reversal between 

 .Adelaide ( + ) and Sydney (Nova Scotia) (- ?). this 

 figure shows also, to serve as examples, curves for 

 two other sets of reverse pressure conditions. Thus, 

 Bombay { + ) is compared with the Cordoba (-) 

 pressure curve (inverted), and is an example of the 

 adopted types of pressure variation. Iceland is com- 

 pared with that of the Azores (inverted), and shows 

 the reverse conditions that prevail between a ( + ?) 

 type and a (— ?) type. 



A fact to which attention was very often directed 



