1902.] Short-period Pressure Variation over Large Areas. 135 



region on both sides of the equator, it was important to study the 

 extent of the region in the New "World in which pressure variations 

 similar to those of Cordoba had been recorded. 



As Cordoba represents an area south of the equator, a portion of 

 the United States of America was taken as typifying an area with 

 north latitude and in about the same longitude, and a commencement 

 was made along the lowest available parallel of latitude. This was 

 rendered possible by the kindness of Professor F. Bigelow, of the 

 Weather Bureau, who very generously forwarded proof-sheets of a 

 new reduction of the pressures of many stations. We wish to take 

 this opportunity of expressing to him our best thanks. 



Treating these pressures in the same way as those formerly in- 

 vestigated in the Indian region, several stations which had the best 

 record were chosen. A graphical representation of the variations of 

 four of these stations (Mobile, Alabama ; Jacksonville and Pensacola, 

 Florida; San Diego, California) is given in Plate 2, and for the sake 

 of comparison the pressure of Cordoba, with the inverted curves 

 representing the Bombay pressure and solar prominence variation. 

 This series of curves refers in all cases to the variations of the means 

 of the high pressure (winter) months (October to March in most cases). 

 At Cordoba, which has a southern latitude, the high pressure months 

 extend from April to September. 



The result of the comparison shows that in this region of the world 

 we have a large area, the pressure variations of which are strikingly 

 similar to, but are the inverse of, those recorded in nearly the anti- 

 podal part of the globe. 



The facts observed are so suggestive that we are continuing the 

 inquiry by collecting and discussing observations made in other areas. 



Although the general agreement between the two main sets of 

 curves is most striking, there are minor differences which probably, 

 as stated in the previous paper, will eventually help us to determine 

 those cases in which the prominence effects on pressure are masked 

 by some special local conditions. It may be added that the available 

 observations of prominences refer more directly to their quantity than 

 to their intensity. 



We wish to express our thanks to Mr. W. N. Shaw, F.B.S., who kindly 

 placed the records of the Meteorological Office at our disposal • and to 

 Mr. Hodgson, who has extracted the requisite data from the available 

 records of pressure, and constructed some of the curves. 



