AND THE PREVAILING WINDS OVER THE GLORE. 577 



applied for daily range or for height. For places, for which the means were 

 obtained corrected for daily range, "red." (meaning reduced to mean daily 

 pressure), is entered in Table I. in the column of Hours of Observation. Those 

 stations for which the means are reduced to sea-level are printed in italics. 



The next step was to apply to the figures in Table I. corrections (1) for daily 

 range and (2) for height. So far as possible, that hour, or those hours, of 

 observation were selected when the pressure of the atmosphere is nearly the 

 mean of the day. For places for which this could not be done, a collection of 

 Mean Hourly Variations of the Barometer was made from a considerable number 

 of stations in different parts of the world. From these, approximate corrections 

 for daily range were deduced, and applied to the monthly means of the stations. 



For reducing to sea-level, a table was prepared from the Formula and Table 

 XVI, given in Guyot's Meteorological and Physical Tables, D, p. 89. This table, 

 calculated for each 5° Fahr. of the temperature of the air, from — 40° to 90°, 

 was used in all cases where the height did not exceed 800 feet. For higher 

 situations, the reduction was made by means of Dippe's method, as detailed in 

 Guyot's Tables, D, p. 60. 



The means,* so corrected, were then entered on large polar projections of the 

 northern hemisphere, from which the isobars were drawn for every tenth of an 

 English inch of pressure. The isobars for the southern hemisphere were drawn on 

 charts of Meroator's Projection. The whole was ultimately transferred to charts 

 of the projection on Plates XXV. to XXVII. The isobars, indicating a pressure of 

 30 inches, which is nearly the average pressure, and upwards, are represented on 

 the charts by heavy lines, and lower pressures are represented by light lines. 



For many of the means I have been indebted to the labours and writings of 

 Dove, Buys Ballot, Secchi, Carl Jelinck, Mohn, James, Quetelet, and 

 Kuppfer. For the means of single stations and groups of stations, I have 

 received most valuable assistance from Meteorologists in all parts of the world, 

 for which I beg to return them my grateful thanks. 



Distribution of Atmospheric Pressure, in December, January, and February. 

 — In these months, the highest pressures are grouped over the land portions of 

 the northern hemisphere, and the larger the extent of the land the greater is 

 the pressure. The area of high barometer (30 inches and upwards) embraces 

 nearly all Asia ; all Europe, south of the North and Baltic Seas ; the North Atlantic, 

 between 15° and 45° lat. ; the West Indies ; North America, except the north and 

 north-west ; and the North Pacific, between 8° and 24° lat. There are also two 

 regions of high pressure of comparatively small extent — the one in the South 

 Atlantic, and the other in the South Pacific. 



* The original observations are given in Table I. in preference to the corrected means deduced 

 from them. 



