Anticyclones and S.A. Weather. 51 



synchronous charts of the isobars. A very decided result was 

 obtained. Without exception the anti-cyclones lay over those parts 

 of the Atlantic where the temperature of the sea was lower than that 

 of the air, whereas the cyclonic systems were confined to those parts 

 where the temperature of the sea was higher than the shade 

 temperature of the air. Further, where the strongest contrasts of 

 temperature prevailed, there would be located the core or centre of 

 the anti-cyclonic system. Numerous instances were found in which 

 the core of the system would move away from a locality, losing 

 intensity as it did so, but as it returned to the same spot many days 

 afterwards it would gradually increase to its original intensity, and 

 resume its control over all the weather conditions in the 

 neighbourhood. Applying these results to the progressive movements 

 of anti-cyclones, generally, we have strong reasons for believing that 

 anti-cyclones wall by preference move to those localities where they 

 will find the surface temperature of either sea or land colder than that 

 of the air above it ; and will follow more readily such a track, from 

 the extreme summer to the extreme winter position, as affords a 

 maximum of these congenial conditions. This is one of the reasons 

 why the track must vary in different years, especially when it leads 

 across mountain ranges on which the snow lies longer in some years 

 than in others, or across districts to which rivers bring the rainfall 

 from a distance, and in varying quantities. 



At the Bristol meeting of the British Association in the summer 

 of 1898, Mr. Douglas Archibald brought to notice a set of 20 types 

 of weather systems which had been found to prevail over a great part 

 of the northern hemisphere. They were the result of an exhaustive 

 examination of synoptic charts by Professors Van Bebber and 

 Koppen, and they excited considerable attention, because their authors 

 were able to announce that not only do such types persist for 4 days 

 on an average, but that they exhibit a tendency to succeed one another 

 and to be associated in some cases with one another. In preparing 

 the types, they had analysed charts extending over several years, 

 tabulating the number of days each type had appeared, and the 

 number of times and the manner in which the types had been 

 associated amongst themselves. In this way it was proved that some 

 of the types belonged to certain seasons, and would at some seasons 

 precede, and at others follow, those with which they were most closely 

 allied. On looking through the author's original work for an 

 explanation of these points, I found that they had attempted none. 

 They had made an analysis of very great value and had left any 

 lessons to be drawn from it to others. Coming so shortly after the 

 paper I had read before the Royal Meteorological Society in July of 

 the same year on the progressive movements of anti-cyclonic systems, 

 it had a special interest for me. It offered a chance of testing the 

 theory in a conclusive manner. If the types which w^ere found to 

 precede those they were allied with at one season, proved on 

 examination to return after a sufficient interval and follow^ the same 

 types at a succeeding season, such a fact would be a strong con- 

 firmation of the existence of a regular succession of types controlled 



