Barometric variations of long duration over large areas

In a paper* communicated to the Society in the year 1902, Sir Norman Lockyer and I pointed out the existence of a barometric see-saw of short duration† (about 3·8 years) occurring between two large regions, nearly antipodal to each other, the centres of which were approximately India and Cordoba (South America). A continuation of the research indicated that this barometric see-saw was of greater extent than was at first supposed, and in a further communication‡ in the same year observations extending over new regions were discussed and the results published. Still further inquiry indicated that this see-saw was almost world-wide in its extent, and the result of a later investigation, which included the examination of pressure observations at 95 stations scattered over the earth’s surface, was communicated§ to the Society in the year 1904. During the progress of this work it was noticed that many of the curves representing barometric changes over a great number of years in various widely distributed areas exhibited variations of much longer duration which were neither coincident in their epochs of maxima or minima or even in the lengths of their oscillations.