Report on Marine Meteorological Observations. 369 



meridians and parallels, and to a particular month, is too obvious 

 to require to be further dwelt upon. The distances apart of the 

 meridians and parallels will require to be varied in different parts 

 of the globe, so that the magnitudes of the spaces which they 

 enclose, and for each of which a table will be formed, may be 

 more circumscribed, when the rapidity of the variation of the par- 

 ticular phenomenon to be elucidated is greatest in regard to 

 geograjjhical si>ace. Their magnitude will also necessarily vary 

 with the number of observations which it may be possible to collect 

 in each space, inasmuch as it is well known that there are extensive 

 portions of the ocean which are scarcely ever traversed by ships, 

 whilst other ];ortions may be viewed as the highways of a constant 

 trafhc. 



'I'he strict comparability of observations made in different ships 

 may perhaps be best assured, by limiting the examination of the 

 instruments to comparisons whicli it is proposed to make at the Kew 

 Observatory, before and after their employment in particular ships. 

 From the nature of their construction, the barometers with which 

 Her Majesty's navy and the mercantile marine are to be sujjplied 

 are not very liable to derangement, except from such accidents as 

 would destroy them altogether. Under present arrangements they 

 will all be carefully compared at Kew before they are sent to the 

 Admiralty or to the Board of Trade ; and similar arrangements may 

 easil}' be made bj^ which they may be returned to Kew for re-examina- 

 tion at the expiration of each tour of service. The comparison of 

 barometers when embarked and in use, with standards, or supposed 

 standards, at ports which the vessels may visit, entails many incon- 

 veniences, and is in many respects a far less satisfactory method. 

 The limitation here recommended is not, however, to be understood 

 as applicable in tlie case of other establishments than Kev/, where 

 a special provision may be miade for an equally careful and correct 

 examination. 



At land stations, in addition to proper measures to assure the 

 correctness of the barometer and consequent comparability of the 

 observations, care should be taken to ascertain by the best possible 

 means (independently of the barometer itself), the height of the 

 station above the level of the sea at some stated locality. For this 

 purpose the extension of levels for the construction of railroads will 

 often afford facilities. 



It may be desirable to indicate some of the localities where the 

 data, which tables such as those which have been spoken of would 

 exhibit, arc required for the solution of problems of immediate 

 interest. 



1". It is known, that, over the Atlantic Ocean, a low mean 

 annual pressure exists near the equator, and a high pressure at the 

 north and south borders of the torrid zone (2.')'' to 30° north and 

 south latitudes) ; and it is probable that from .similar causes similar 

 phenomena exist over the corresponding latitudes in the Pacific 

 Ocean : the few observations which we j)ossess are in accord with 

 this supposition ; but the extent of space covered by the Pacific is 



