934 



to an inch of mercury ; nevertheless in the Cyclones, or rotatory 

 storms, there occurs at times a range of pressure of nearly two inches 

 of mercury within forty-eight hours ; but it is shown from a compa- 

 rison of the simultaneous records on board ship, where these great 

 depressions were noted, with the records at the observatories on shore, 

 that the great depressions occurred within very limited areas. 



The author had formerly shown that the times or turning-points 

 of ebb and flow (if the term be permitted) of the aerial ocean, 

 were occasionally retarded or accelerated, although the means fixed 

 the turning-points within certain limit hours ; but he was not then 

 aware that in the ebb or flow of the four daily tides,- they ever 

 retrograded or halted in their onward or retiring course. The hourly 

 observations now show that abnormal conditions are of no infre- 

 quent occurrence,— -that the tides at times flow or ebb for four, 

 five, six or even seven and eight hours (one instance at Aden of 

 nine hours), — that frequent instances occur of retrograde move- 

 ments for short' periods of time, as if the tide had met with a check 

 and been turned back; and at the turning-points there are numerous 

 instances of the atmosphere being stationary for a couple of hours. 



The maximum pressure of the atmosphere is in the coldest months, 

 December or January, but the minimum pressure is not in the 

 hottest months, but in June or July. The barometric readings, 

 when protracted, show a gradual curve from December or January 

 descending to June or July, and then ascending again to December 

 or January, there being an occasional interruption in October or 

 November. As the curves at Madras, Bombay and Calcutta, 

 correspond, and as Madras has 710 south-west monsoon, while 

 Bombay has a south-west monsoon, and is destitute of the north-east 

 monsoon of Madras, it would appear that the general movements of 

 the atmosphere are little influenced by any conditions of its low^er 

 strata ; but the curve of pressure would seem to have some relation 

 to the sun's place in the ecliptic. 



The normal conditions of daily temperature are, that it is coldest 

 in India at sunrise, and hottest between the hours of 1 and 3 p.m. ; 

 but the tables show many aberrations from this rule. The re- 

 gular increment or decrement of mean m.onthiy heat from the maxi- 

 mum or minimum period is somewhat remarkable, as the curve is 

 independent of the south-west monsoon at Bombay and the north- 

 east monsoon at Madras ; and the passage of the sun twice over 

 both places does not derange the curve. The anomalies of the 

 annual mean temperature of Madras, Bombay, Calcutta and Aden, 

 not diminishing \Y\t\\ the increase in the latitude of the respective 

 places, are pointed out, and numerous instances are given of the 

 very great power of the slanting rays of the sun beyond the tropic. 

 As is the case with the barometric, so do the heat tables indicate 

 that the annual and daily ranges of the thermometer diminish vvith 

 the elevation of the place of observation above the sea-level, the 

 elevated table-land of the Deccan however being an exception to 

 this rule. At Mahabuleshwur, at 4500 feet, the temperature of the 

 air was never below 45° with a maximum and minimum thermo- 



