via THE VOYAGE OF H.M.S. CHALLENGER. 



ception and explanation of meteorological phenomena ; and accordingly 

 when the Challenger Expedition was fitted out, arrangements were made 

 for taking, during the cruise, hourly or two-hourly observations. These 

 observations, which are published in extenso in the Narrative of the Cruise, 

 Vol. II. pp. 305-744, are by far the most complete yet made of the 

 meteoroloirv of the ocean. 



As is well known, elaborate observations were also made on deep-sea 

 temperatures, which gave results of the first importance in terrestrial 

 physics, and opened for discussion the broad question of oceanic circulation, 

 on a sound basis of well-ascertained facts; but a right understanding of 

 this subject demands, in the first place, a full discussion of atmospheric 

 phenomena. Now any such discussion requires, for its proper handling, 

 maps showing for the months of the year the mean pressure, mean 

 temperature, and prevailing winds of the globe, with extensive tables from 

 which these data have been obtained. The only works available were 

 Dove's Isothermals, 1852; Buchan's Isobars and Prevailing Winds, 186V) : 

 and Coffin's Winds of the Globe, 1875 ; x all of which were based, necessarily 

 when written, on defective data. This remark applies more particularly 

 to the vitally important element of the prevailing winds, which were based 

 on observations in very many cases too short continued to give good 

 averages. 



A re-discussion of all the available information regarding the different 

 atmospheric phenomena, with special reference to the Challenger obser- 

 vations, was therefore most desirable ; this work was undertaken in 

 1882, at my request, by Mr. Alexander Buchan, and since that date, 

 upwards of seven years, it has occupied most of his time with that of his 

 assistants. The data thus collected and prepared are given in the nine 

 Tables of the Appendices to this Report, of which the more important 

 are the mean diurnal variation of atmospheric pressure at 147 Stations, 

 the mean monthly and annual pressure of the atmosphere at 1366 Stations, 

 and a similar table of temperature at 1620 Stations, and the mean monthly 

 and annual direction of the wind at 746 Stations. These Tables may be 



1 Dove, On the Distribution of Temperature over the Globe, 1852, and for N. Hemisphere, 18G4 ; 

 Buchan, On the Mean Pressure of the Atmosphere and Prevailing Winds over the Globe, Trans. Roy. Soc. 

 Edin., vol. xxv. p. 575, 1869 ; Coffin and Woeikof, On the Winds of the Globe, Smithsonian Contributions 

 to Knowledge, 1875. 



