456 



THE PHYSICAL GEOGRAPHY OF THE SEA. 



The low austral ba- ^'^^^^'^^^g the expeditions to the South Seas in 1839- 

 rometpr. 4]^^ \^^^ occasiou to lemaik upon the apparent de^ 



ficiency of atmosphere over the extra- tropical regions of the south- 

 ern hemisphere ; and the low barometer off Cape Horn had at- 

 tracted the attention of navigators at an early day. I observed 

 it in 1831 when doubling the Cape as master of the U. S. S. Fal- 

 mouth, and wrote a paper on it, which was published in the 

 American Journal of Science in 1833-4. The more abundant 

 materials which the abstract logs have placed within my reach 

 (>nable me to go more fully into this subject. To ascertain wheth- 

 er these ^^ barometric aiiomalies^^^ as they are called, are peculiar to 

 the regions about Cape Horn, or whether they are common to 

 high southern latitudes in all longitudes, the observations about 

 Cape Horn were arranged in one group ; those between 20° W. 

 and 140° E. in another ; and those between 140° E. and 80° W. 

 in another, with the following results. (They are all on the polai- 

 ^ideof40°S.) 



Mean Height of the Barometer, as observed beticeen 



857. The instruments used for these observations were for the 

 Discussion of observa- i^^st part the old-fashioucd marine barometer, to 



lion 



which no corrections have been applied. The dis- 

 crepancies of this table evidently arise from the lack of numbers 

 sufficient to mask these sources of error, or from the influence of 

 the land, and not from any difference as to the mean height of 

 the barometer along the same parallels at sea in any one of the 

 three divisions. In this discussion, the observations of each group 

 and every band were arranged according to the month. These 

 monthly tables are not repeated here, but they do not indicate 

 any decided change in the barometric pressure in high southern 

 latitudes according to the season. The barometer there stands 

 low the year round. 



