AND METEOROLOGY OF DUKHUN. 173 



Mr. Hudson however, at the Royal Society, in his careful hourly observations even 

 in the high latitude of London, found it amount to "0120 ; and I feel assured that 

 further observations will establish its existence at those places rendered doubtful by 

 the data just quoted. 



With respect to the exact periods of the diurnal flux and reflux, and the duration 

 of the quiescent state of the atmospheric tides, the subject has been wholly over- 

 looked, as far as I can learn, in Western India ; but even had it not escaped atten- 

 tion, there have not been, I believe, instruments in use sufficiently delicate in their 

 construction to read off" very small quantities. Dr. Walker at Mahabuleshwur, Cap- 

 tain Jervis in Bombay, at the Engineer Institution, and myself, are the only persons 

 who have made observations on the tides. For myself, my multitudinous avocations 

 deprived me of the necessary leisure for some years to enable me to enter systemati- 

 cally into the inquiry. Occasionally, at the admitted limit hours of the diurnal oscil- 

 lations of the barometer, I made a few observations ; but they were of little further 

 value than to show that the maxima and minima, on consecutive days, did not occur 

 at the same exact period of time. In 1830, however, with two of Englefield's baro- 

 meters, which admitted of the adjustment of the lower level of the mercury to the 

 1000th of an inch, I made observations every quarter of an hour, and sometimes every 

 five minutes, during the whole of the year at the limit hours of the diurnal maximum 

 and minimum a.m. and p.m. and maximum p.m. tides. Messrs. Walker and Jervis 

 had in use Gilbert's barometers, and did not observe for the exact limit hours. 



Messrs. Boussingault and Rivero, in addressing Humboldt from South America, 

 state that their labours had verified the fact established by Humboldt, that the mer- 

 cury between the tropics attains its maximum between 8 and 1 a.m., then descends 

 till near 4 p.m., and is at the minimum between 3 and 5 p.m. : then it ascends till 1 1 

 at night, without reaching however the same height at which it was at 9 in the morn- 

 ing, and finally re-descends till 4 in the morning. It will be seen how closely these 

 limit hours hold good in Dukhun as well as in America ; and Mr. Hudson has de- 

 termined that they hold good in London : but I have on record instances of the 

 barometer rising until 10^ 45™ a.m., falling until 6 p.m., and rising until 12 at night ; 

 but the instances are rare : and even the tremendous storms preceding and closing 

 the monsoons in India only modify and do not interrupt the tides *. Humboldt ob- 

 serves, that in Macao, in 1814, there were frequent tempests, and twenty-six stormy 

 days, and yet there was not a single instance of the tides being interverted. He says 

 also, that in reviewing the whole of his observations made at different heights, and 



* The variations appear to be independent of those of temperature and the seasons. If the mercury was 

 descending from 2'' till 4'', or rising from 4'' till IP, a violent storm, an earthquake, showers, and the most 

 impetuous winds, would not alter its movement, which nothing appears to determine but the real time or the 

 position of the sun. — Humboldt, Personal Narrative, vol. vi. part ii. p. 701. 



Humboldt further remarks that the hurricanes (in the West Indies) are not in general accompanied by such 

 an extraordinary lowering of the barometer as is imagined in Europe. Captain Don Thomas de Ugartb, on 



