1904.] Short-Period Atmospheric Pressure Variation. 459 



and 7 are given the groups of months (whether high or low pressure 

 months) in each case for which the pressure curves examined afforded 

 the greatest resemblance to the types which form the basis of the 

 classification. In cases in which the curves of the mean yearly values 

 alone have been utilised, these columns have been left blank and 

 reference made in the column headed " General Remarks." 



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 ( + f) type, the British Isles, Germany, and Spain of the ( ± 1) type, 

 and the Azores of the ( - 1) type. From a glance at the accompanying 

 plate (Plate 12), which shows the relation to each other of some of the 

 pressures over these areas, the changes from a ■ ( - ?) to a ( + f) type 

 can be observed. 



It will be seen that although practically the same groups of months 

 have been taken in each case, pressure in excess of the mean value in 

 Greenland or Iceland corresponds to a deficiency of pressure over the 

 area covered by Great Britain, Austria and Spain, the curves being 

 in the main the reverse of each other. Again, the pressure curve for 

 the Azores follows more nearly the ( - ) type, as will be seen by 

 comparing it with the Cordoba curve, but it has a certain similarity 

 to those of Madrid, Vienna, etc., to which it must therefore be closely 

 connected. 



While the western portion of Europe is of this ( ± 1) type, the 

 eastern portion gradually assumes the ( - V) type, and this region 

 extends not only probably to Norway and Sweden, but right across 

 European and 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 1877. 



The inverted curve for the latter with the Adelaide (Australia) 

 pressure curve for comparison is shown in an accompanying plate 

 (Plate 13). 



In addition to illustrating this reversal between Adelaide ( + ) and 

 Sydney (Nova Scotia) ( - f), this plate shows also, to serve as examples, 

 curves for two other sets of reverse pressure conditions. Thus 



