5© Report S.A.A. Advancement of Science. 



Daily weather charts had made us familiar with the progressive 

 movements of subsidiary, small, anti-cyclonic systems, and, 

 theoretically, there was no reason why the larger and more persistent 

 systems, which had shown themselves capable of resisting for weeks 

 at a time all efforts to break them up, should not move off, rather than 

 disperse, when the conditions became unfavourable. If it should 

 prove that they had a progressive movement, it was natural that 

 their persistence at the extreme ends of their swing should attract 

 attention, for they would appear to linger there, in going and 

 returning, for a longer period than anywhere else in their journey. 

 All available weather charts from 1876 onwards were accordingly 

 examined, and for the 11 years, 1 881 -91, the mean monthly positions 

 of the cores, or centres, of the Siberian and Atlantic systems were 

 plotted whenever sufficient information could be obtained. The 

 conclusion arrived at was that there was a distinct progressive seasonal 

 movement. In the case of the Siberian system this was to the west 

 in the early months of the year, and to the east in the later months, 

 and the persistence which had been observed to occur annually in 

 winter for such a long time over Eastern Siberia was, as anticipated, 

 in consequence of its reaching the extreme end of its swing whilst in 

 that district. The Atlantic system showed a movement on to and off 

 the land, according to the seasons. This fact will be found to 

 be one of special interest to us when we come to consider similar 

 movements off and on to the land in the southern hemisphere. 

 A-nother important feature was disclosed by the examination. The 

 tracks followed by the Siberian system were not the same each year, 

 nor was the date of arriving at and leaving the extreme winter and 

 summer positions the same. There were good grounds for thinking 

 that the track was deflected north and south of a mean or average 

 track till it reached a maximum, when it gradually returned to the 

 mean again ; and, further, that the date of reaching the extreme 

 limits of its swing was sometimes before, and sometimes after a mean 

 or average date. The whole of the movements seemed to be governed 

 by some law of which we have no conception whatever, and in no case 

 were the successive deviations from the mean abrupt. One principle 

 seemed to govern not only the movements, but the formation of the 

 Various anti-cyclonic systems. Wherever strong contrasts of tempera- 

 ture were found to be set up from any cause, atmospheric conditions 

 resulted which gave rise to anti-cyclonic systems and largely 

 controlled their movements. It was not difficult to find numerous 

 charts by which to put this to the test. In the " Synchronous 

 Weather Charts of the North Atlantic " for the period August ist, 

 1882, to September 3rd, 1883, we have a daily record of the isobars, 

 the isotherms of air and water, and the resultant weather, and with 

 the help of these an examination can be made under the most 

 favourable conditions of anti-cyclones and their movements. Access 

 was accordingly obtained, by leave of the Royal Society, to the 

 original ships' records from which the charts were compiled. The 

 difference between the shade temperature of the air and of the sea 

 at noon was plotted, and a comparison made with the completed 



