OBSERVATIONS TAKEN IN INDIA. 
319 
It has been asserted that when the barometer is corrected for moisture its diurnal 
movements in the tropics are resolvable into a simple ascending and descending 
curve in the twenty-four hours, nevertheless the first feature of the Table is the 
existence of two ascending and two descending tides, although the correction for 
moisture had reduced the air in which the mercurial column had moved to a sup- 
posed dry state. The usual hours of the ebb and flow are generally sufficiently mani- 
fest, particularly in the hours of greatest pressure, yet there is the unusual circumstance 
of the ascending a.m. tide turning in five months at 6 a.m. instead of 9 — 10 a.m., and 
in this tide also there are three instances of a check to its usual movements. The 
ascending p.m. tide has also its anomalies. In eight months it attained its maximum 
at the usual time between 9 and 10 p.m., but in July there is the rare circumstance 
of its turning at 5 p.m. instead of 9 — 10 p.m., and in June and August the equally 
rare circumstance of its turning at 7 p.m. ; the next anomaly in this tide is in October, 
when it did not turn until midnight. The chief anomalies, as at Madras, Bombay and 
Dodabetta, occur in the a.m. and p.m. ebb or descending tide. The Table shows that 
the turning-points of the p.m. diurnal ebb, ranged from noon in February, and July, to 
4 p.m. in April and June. In February, when the minimum occurred at noon, the 
maximum took place at the usual hour, 10 p.m. ; there was therefore the almost un- 
precedented circumstance of a tide continuing to flow for nine hours. In the a.m. de- 
scending or ebb tide, the anomalies are even more marked than in the corresponding 
P.M. tide, for the turning-points range from 1 a.m. to 5 a.m. In January it turned at 
1 A.M., and then the ascending tide continued to flow uninterruptedly until 10 a.m., a 
second instance of a nine hours’ flow . In July, September and November, it also 
turned at 1 a.m., but the maximum occurred at 6 a.m. instead of 10 a.m., the flow in 
each of these months being five hours ! a glance of the eye over the Table will show ; 
although the different tides ultimately attained their respective maxima and minima, 
yet in many instances they were subject to checks or interruptions, which appeared 
to give way after a short resistance to the periodic movements of the atmosphere. 
In the month of August, however, the atmosphere appeared in so vacillating and 
disturbed a state, that the only tide which turned at the normal hour was the 10 a.m. 
maximum tide. The means of the hourly readings on four days in each month, 
corrected for moisture, give a mean curve of pressure in each month which nearly 
corresponds with the curve of pressure of the daily readings of the barometer cor- 
rected for temperature only. The maximum pressure with both corrections occurs 
in December, but the minimum occurs in June corrected for temperature and in July 
with both corrections. The whole of the facts connected with the meteorology of 
Aden of which I have made use, are from observations taken by Sergeant Moves, 
with excellent instruments, and Dr. Buist is now passing the observations through 
the press. 
These facts, which could be very greatly multiplied, have been somewhat dwelt 
upon, with a view to a right understanding of Humboldt’s observations in his Cosmos*. 
* Bohn’s Edition, vol. i. p. 320. 
