Meteorological Journal kept at Scringapatam. 251 



must be the principal source of the vapour, being 77, and the 

 probable dew point 63", then .966 — .615 = .351 of an inch, 

 the depth of water evaporated in twenty-four hours, or 128 

 inches yearly.* The degree of dryness on the thermometer will 

 be therefore 14°. The degree of moisture on the natural scale 

 of the hygrometer .636, 1.000 being perfect dampness; and 

 the weight of a cubic foot of vapour, 6.5%% gr. 



The prevailing winds are the N. E. and S. W., or the gene- 

 ral monsoons of the Indian Ocean. The S. W. sets in during 

 the month of April. When it first commences, its reciproca- 

 tion with the N. E. interrupts the serenity of the weather, and 

 during its continuance thunder storms occur almost every 

 day, with heat, — lightning at night. This is the rainy sea- 

 son, but the monsoon having deposited its superabundant 

 moisture upon the Ghauts, very little rain falls at Seringa- 

 patam. During the N. E., which begins about the end of Oc- 

 tober, the weather is settled and fine, with heavy dews before 

 sunrise. 



Results for the Year 1814. 

 I have arranged the numerical results of this year under 

 (A) Table I. The temperature was considerably higher than 

 in 1816. The mean temperature at sunrise = 64.65; in the 

 afternoon 92.1, mean temp. 78.4. Mean temp, of the day 

 85.2 ; of the night 71.52 ; of the coldest month 72.6 ; of the 

 warmest 86.5 ; 



* Mr Anderson has observed that in settled weather the minimum tem- 

 perature of the night does not fall below the term of precipitation taken at 

 sunset, or in the evening ; and a variety of experiments made at Leith 

 have proved the general truth of the principle. Since the temperature at 

 sunrise will be a very little above the minimum by a register thermo- 

 meter, and since the constituent temperature of the vapour varies very 

 little during the day, there cannot be a great error in assuming the tempera- 

 ture at sunrise to correspond with ths mean point of deposition. Dr 

 Young has shown that the mean evaporation in twenty-four hours is ex- 

 pressed by the height of a column of mercury equivalent to the elusticity 

 of the vapour, and the effect of the moisture in the atmosphere may be 

 allowed for by deducting the tabular number of the elasticity at the dew 

 point. The evaporation at London, calculated in this way by Mr Daniell, 

 accords in a remarkable manner with the amount observed by Mr How- 

 ard. 



