of Edinburgh, Session 1866-67. 
303 
Monday, 1 bth March 1868. 
Dr CHRISTISON, Vice-President, in the Chair. 
The following Communications were read 
1. The Mean Pressure of the Atmosphere over the Globe for 
the Months and for the Year. Part I.— January, July, 
and the Year. By Alexander Buchan, M.A., Secretary to 
the Scottish Meteorological Society. 
The three charts which were exhibited, showing, by isobarometric 
lines, the mean atmospheric pressure over the globe, during January, 
July, and the year, were constructed from observations made at 
358 places thus distributed over the earth, — 167 in Europe; 51 in 
Asia; 22 in Africa and adjoining islands ; 35 in South America, 
West Indian Islands, and Atlantic ; 63 in North America; and 20 
in Australasia and Antarctic Ocean. Of the European stations, 
12 are in Scotland, 14 in England, 27 in Austria, 12 in Italy, 10 in 
France, 10 in the Netherlands, 9 in Norway, and 57 in the Russian 
empire, &c. The list might have been largely increased ; thus 
a larger number might have been given from the 80 Scottish 
stations ; but the ] 2 given were judged sufficient to represent the 
mean atmospheric pressure of this country. 
In the British islands the means were uniformly taken for the 
ten years from 1857 to 1866, in order that they might be strictly 
comparable with each other ; and the means of several European 
stations were calculated for the same year. In the United States 
of America the means were uniform for the six years from 1854 to 
1859. In selecting the stations, respect was had to the obtaining 
of a good mean, — that is, observations for a sufficient number of 
years to show, as nearly as possible, the true mean. For example, 
at Bombay, from 1847 to 1860, the lowest mean for July was 
29*598 inches in 1851, and the highest 29*673 in 1853. This re- 
gularity in the pressure of the same month, from year to year, is a 
feature common to all tropical countries ; and hence, in such places, 
a few years were accepted as a srood mean. On the other hand, 
VOL. vi. 2 r 
