of the South African Institution. 38'J' 



3r(l. Tliat this daily oscillation is itself subject to an aiimial 

 alternate increase and diminution, — the limits being . 0198 in. 

 and . 0322, the former or lesser diurnal variation corresponding 

 to the middle of January, and the latter or greater to the be- 

 ginning of July. 



4th. That these fluctuations are maintained with such re- 

 gularity that there is not a single month in the 58 examined, 

 in the mean of which the daily oscillation does not appear, — 

 and that in the annual ORcillation (with exception of one re- 

 markable anomaly, produced by the tremendous storm of July 

 1831) not only does every year exhibit the fluctuations in 

 question, but its progress is marked by similar stages, or 

 phases of increase and diminution ; the most remarkable cf 

 which is a temporary suspension of the regular, rapid rise of 

 the mercury towards its maximum, usually taking place about 

 the latter end of May or beginning of June. 



5th. That, contrary to usually received notions — the rainy 

 season at the Cape corresponds to a generally elevated state 

 of the Barometer — although it is true that particular storms 

 of wind and rain are often marked by a temporary depression. 



Sir J. Herschel further observed, that the amount of the 

 Annual Barometric variation at the Cape corresponds pretty 

 nearly with the amount of a depression of the mercury which 

 he stated to have been observed by himself in his voyage 

 hither, at and near the Equator, below its habitual state in 

 the extratropical regions, — a depression then noticed as he at 

 that time supposed for the first time, but which it appears had 

 also been (very recently) noticed and made the subject of 

 inquiry and numerical computation by Professor Schow of 

 Copenhagen, in a paper published in the Annates de Chinie for 

 June 1833. 



Sir J. H. also further stated that the mean Annual Barome- 

 tric fluctuation at Calcutta, on the average, of between two 

 and three years observations made by Mr. Prinsep, examined 

 by him, appears to be much greater than that at the Cape, 

 and what is very remarkable, in a contrary direction, the 

 Maximum of Calcutta corresponding to the Minimum at the 

 Cape. And he attributes this to an actual bodily transfer of a 

 portion of air from hemisphere to hemisphere, by the alternate 

 heating and cooling of the two hemispheres as the Sun crosses 

 from side to side of the Equator. The effect of this cause 

 which he considers to be general over the whole Earth, will be 

 to modify the regular and constant effects of the trades by a 

 set of periodical winds differing materially in their character 

 fiom local monsoons, and to this cause he is disposed to attri- 

 bute tlie observed annual oscillation of the extreme North and 

 Sjouth limits of the Trade winds. 



