Report on Marine Meteorological Observations. 373 



pressure into its two constituent pressures would give direct and 

 conclusive evidence of the cause to vv'hich such a barometric 

 variation should be ascribed. It would also follow, that evapo- 

 ration being greatest in the south, and condensation greatest in 

 the north, the water which proceeds from south to north in a state 

 of vapour, would have to return to the south in a liquid state, and 

 might possibly exert some discernible influence on the currents of 

 the ocean. The tests by which the truth of the suppositions thus 

 advanced may be determined, are the variations of the meteor- 

 ological elements in difterent seasons and months, determined by 

 methods and instruments strictly comparable with each other, and 

 arranged in such tables as have been suggested. A still more 

 direct test would indeed be furnished by the fact (if it could be 

 ascertained), that the quantity of rain which falls in the northern is 

 greater than that which falls in the southern hemisj)here ; and by 

 examining its distribution into the different months and seasons 

 of its occurrence. Data for such conclusions are as yet very insuf- 

 ficient ; they should ahvays, however, form a part of the record at 

 all land stations where registers are kept. 



In order that. all observations of the elasticity of the aqueous 

 vapour may be strictly comparable, it is desirable that all should be 

 computed by the same tables ; those founded upon the experiments 

 of i\IM. Reguault and Magnus may be most suitably recommended 

 for this purpose, not only on their general merits, but also as being 

 likely to be most generally adopted by observers in other coun- 

 tries. 



Temperature of the Air. 



Tables of the mean temperature of the air lu the year, and in the 

 different months and seasons of the year, at above 1000 stations on 

 the globe, have recently been computed by Professor Dove, and 

 published under the auspices of the Royal Academy of Sciences 

 at Berlin. This work, — which is a true model of the method in 

 which a great body of meteorological facts, collected by different 

 observers and at different times, should be brought together and 

 coordinated, — has conducted, as is well known, to conclusions of 

 very considerable importance in their bearing on climatology, and 

 on the general laws of tiic distribution of heat on the surface of the 

 globe. These tables have, however, been formed exclusively from 

 observations made on land. For the completion of this great 

 worlc of physical geography, there is yet wanting a similar investi- 

 gaticm for tlie oc> ante portion ; and this we may hopefully anticipate 

 as likely to be now accomplished by means of the marine observa- 

 tions about to be undertaken. In the case of the temperature of 

 the air, as in tiiat of the atmospheric pressure previously adverted 

 to, the centres of geograj)hical spaces bounded by certain latitudes and 

 longitudes will form points of concentration for observations, which 

 may be made within tiiose spaces, not only by the same but also by 

 different ships ; provided that the system be steadily maintained of 

 employing only instruments which shall have been examined, and 



