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



It is right to acknowledge here the invaluable assistance received from the 

 meteorological writings of Dr. Hann, who holds the first place among meteorologists for 

 the importance, extent, and trustworthiness of his contributions to the climatologies of 



the globe. 



In the preparation of the Tables I have been assisted by Mr. H. N. Dickson 

 and Miss J. H. Buchan of the Scottish Meteorological Society's office. Miss Buchan 

 has assisted during the whole time of the discussion. She copied out the whole of the 

 Challenger observations, chronologically arranging them according to subject, and 

 assisted in working out the hourly and other averages ; she also collected and 

 computed a large part of the new wind averages given in Table VII., a considerable 

 proportion of which were laboriously calculated from daily observations, and several even 

 taken from daily curves of wind direction ; and she aided generally in checking the 

 correctness of the computed averages. I had the benefit of Mr. Dickson's help during 

 1887 and 1888. He computed the air temperatures of the North Atlantic from 

 the Bulletin of International Meteorology ; further assisted in the preparation of 

 Table V. ; carried out the work of differentiation for the mean temperatures at a 

 considerable number of places in the Bussian Empire ; charted the greater part of 

 the temperatures ; and prepared the first draught of the isothermals for large portions 

 of the globe. 



THE TEMPERATURE, PRESSURE, AND PREVAILING WINDS OF THE GLOBE. 



These prime elements of climate will, from their intimate relations to each other, 

 be more satisfactorily dealt with together than separately. It is scarcely possible to 

 over-estimate the importance of a knowledge of the distribution of atmospheric 

 pressure, or of the mass of the earth's atmosphere over the globe, in its varying 

 amounts from month to month. Observations prove conclusively that winds are 

 simply the movements of the atmosphere that set in from regions where there is a 

 surplus towards regions where there is a deficiency of air; and the nearer the 

 observations of pressure and wind approximate to true averages, the closer is the 

 relation seen to be subsisting between these two distinct phenomena. Again, since 

 prevailing winds to a large extent determine the temperature and rainfall of the 

 regions they traverse, isobaric maps may be considered as furnishing the key to the 

 climatologies of the globe as well as to many of the more important questions of 

 meteorological inquiry. The distribution of temperature in the atmosphere may be 

 regarded as the fundamental problem of meteorology, seeing that the varying 

 pressures, humidities, and winds are either direct or indirect consequences of the 

 varying distribution of temperature. As regards the distribution of the temperature 

 over the land surfaces of the globe, the problem was approximately solved by the 



