404 Miss E. E. Cave-Browne-Cave. Influence of the [Dec. 20 



the best intervals between the readings in order to find, from the 

 anterior observations at the four stations, the most probable barometric 

 height at A on a given day, and the most probable error of this esti- 

 mate. They thus supply a means of giving to his predictions a greater 

 precision than is at present attainable. It should also be remembered 

 that, although the present paper only deals with barometric observa- 

 tions, the same methods could be applied to temperature, or to any 

 other of the quantities with which meteorology is concerned. 



In order to show that the relations between the two stations mainly 

 considered in this paper are not due to purely local conditions, corre- 

 sponding investigations have been made for two stations in the Southern 

 Hemisphere, St. Helena and Cape Town. Although the shortness of 

 the period (1893-98) for which observations taken at St. Helena are 

 available, prevents these results from being as fully reliable as those 

 obtained for the North American stations, yet they are sufficient to 

 show the general nature of the pressure relationship between the two 

 places, and the influence of the time factor. 



The latitudes and longitudes, and hours of observation are as 

 follows : * 



Halifax, 44 35' N., 63 40' W. ; 9 A.M. 



Wilmington, 33 14' N., 77 59' W. : 7 A.M. up to June 30, 1888, 

 afterwards 8 A.M. 



Cape Town, 34 0' S., 18 35' E. ; 8 A.M. 

 St. Helena, 15 57' S., 5 40' W. ; 9 A.M. 



This gives an arc of about 15 51', or about 1090 miles between 

 Halifax and Wilmington, and 28 18', or about 1950 miles between 

 Cape Town and St. Helena. Roughly speaking, Halifax is north-east 

 of Wilmington, and Cape Town south-east of St. Helena. 



The twenty years of the data for Halifax and Wilmington were 

 divided into two decades, 1879-88 and 1889-98, and the summer and 

 winter months (equinox to equinox) were dealt with separately. As 

 was pointed out in the previous note, there is a marked difference 

 between the summer and winter results, and two ten-year periods were 

 desirable for mutual control. It soon became obvious that the summer 

 and winter time factors were different in character, the interval for 

 maximum correlation being considerably shorter in the summer. The 

 numbers obtained indicate that change of pressure passes from 

 Wilmington to Halifax, i.e., from south-west to north-east, and thus it 



* The Canadian Meteorological Office kindly superintended the copying of the 

 Halifax and other Canadian data, the cost of which was defrayed by Professor 

 Pearson ; the Smithsonian Institution provided the copies of the Wilmington and 

 other United States data ; the readings for Cape Town we owe to the mediation 

 of Dr. W. N. Shaw, who procured them from the Cape Meteorological Committee, 

 the cost of copying them being defrayed by a grant from the Government Grant 

 Committee of the Royal Society. 



