182 LIEUT.- COLONEL SYKES ON THE ATMOSPHERIC TIDES 



Mayer's formula. Ahmednuggur is 1900 feet above the sea with a mean temperature 

 of 78° : the calculated mean temperature is 72°*27. Mhow in Malwa, at 2000 feet, 

 observed mean temperature 74° ; calculated 69°'86. A spring in the hill fort of Hur- 

 reechundurghur I found to be 69°'5 : the calculated mean temperature for the lati- 

 tude of that fort, at an elevation of 3900 feet, is 65°' 45. The calculated mean tempe- 

 rature of Poona is 72°'78 ; the observed IT'I - But I purpose enlarging on this sub- 

 ject in a future paper on the mensuration of heights in Dukhun, determined barome- 

 trically and thermometrically. 



An inspection of my tables of temperature will show that the mean temperature of 

 9^' 30™ A.M. is almost identical with the annual mean temperature deduced from the 

 maxima and the minima. Professor Forbes observes that the same holds good at 

 Edinburgh. To show the importance of position in placing instruments for observa- 

 tions of temperature, in November 1828, I put thermometer No. 2 under a grass roof 

 adjoining the eastern wall of my house, but within twelve feet of thermometer No. 1, 

 which remained in its usual place. The instrument was secure from direct or re- 

 flected heat. At sunrise the mean for the month of No. 2 was 7°' 42 lower than the 

 mean of No. 1 ; at O'' 30™ it was 1°76 higher ; and at 4 p.m. it was 2°-71 higher-, but 

 its mean for the whole month was 2°*35 less than the mean of the thermometer kept 

 in the house near the open window. 



To ascertain the numerical cooling effect of shutting out the external diurnal air 

 from acting upon the thermometer in the hot months, I hung thermometer No. 2, in 

 the month of April 1827, in my drawing-room, communicating by double doors with 

 a large dining-room surrounded by an inclosed and glazed verandah. I had all the 

 external windows and doors carefully shut at 7 a.m. daily, and opened again at sun- 

 set. Thermometer No. 1 was in its usual place in my library, with a free circulation 

 of air. Thermometer No. 2 was 1°*73 higher than No. 1 at sunrise ; at 9^ 30™ a.m. it 

 was 0°-63 Icrwer ; and at 4 p.m. it was 5°'5 loiver ; and the difference of the monthly 

 means was 3°'62 minus in favour of thermometer No. 2. There cannot be a doubt, 

 therefore, of the advantage of closing a room in the tropics during the heat of the day. 



My hygrometric observations with Daniell's hygrometer for forty-three months, 

 from April 1826 until March 1828, and from June 1829 until January 1831, were 

 very complete and satisfactory. The first great feature was the annual mean dewing- 

 point being higher at 9 J a.m. than at sunrise or 4 p.m., excepting in 1829 — 1830 ; but 

 it did not uniformly hold good in each month of the year. In 1826 the mean dewing- 

 points in Dukhun at sunrise and 9j a.m. were respectively 66°'58 and 67°*56 ; tem- 

 perature of air 73°'66 and 77°'53, containing 7*473 and 7*634 grains of water in a 

 cubic foot of air ; but in the monthly means, October had a higher dewing-point at 

 sunrise than at 9 J a.m. : October, however, was the only month in which this occurred. 

 In the mean for 4 p.m., September had a higher dewing-point at 4 p.m. than at 9\ a.m. 

 On the whole, it may be asserted that the mean dewing-points of the three periods of 

 the day were tolerably uniform, although at 4 p.m. there was a much less absolute 



