AND METEOROLOGY OF DUKHUN. 169 



best types of the meteorological phenomena of Dukhun. The fall of the tide from 

 9 — 10 A.M. to 4 — 5 P.M. was -1 166, thermometer +4°'9. Comparing this tide with the 

 same tide observed in other places, we find that at Madras, lat. 13° 5', from observations 

 taken at the Observatory every tenth day in 1823, the mean oscillation was '079, 

 mean range of attached thermometer +8°'5. At Calcutta, latitude 22° 35', the means 

 of the years 1829, 1830, and 1831, make the oscillation amount to '110, thermometer 

 range + 12°'2. At Saharunpoor in Hindoostan, 1000 feet above the sea, latitude 3 1°N., 

 by Mr. Royle's registers, the tide was '120, mean range of thermometer 4-24°-2. At 

 Ava, latitude 21° 51', Major Burney's observations in 1830 make the tide amount 

 to '126, mean diurnal range of thermometer +10°-6. Agreeably to Mr. Prinsep, at 

 Benares, latitude 25° 30', it is "105, range of thermometer attached + 16°'6. Professor 

 Forbes in Edinburgh found the oscillation to be '0114, mean range of thermometer 

 attached for three years — 0°*57. And Mr. Hudson, at the Royal Society in London 

 in 1831, determined the oscillation to be '0289, therm. 4-l°73. 



Humboldt and Bonpland in equatorial America, at Cumana, La Guayra, Payta, 

 Lima, and Rio Janeiro, found the mean extent of the oscillation at most from "0945 

 to -1 181 *. At Lima, latitude 12° 26', it was a little less (-0669 to '0905 f) than nearer 

 to the equator, where it was from '1023 to '1291 J. Boussingault and Rivero in 

 1823-4, at Santa F6 de Bogota (latitude 4° 35' N.), height 8196 feet, found it to be 

 •0905, approaching my mean for 1829. At La Guayra (latitude 10° 36' N.), at the 

 level of the sea, it was '0960 ; but as the preceding observations in America, with the 

 exception of those at Bogota, were for a few days only, they are valueless as indi- 

 cative of the mean diurnal oscillations, much less the monthly and annual means. 

 The extent of the diurnal oscillation from 9 a.m. until 4 p.m. on the table land of 

 Bogota was from -0248 to -1433 §. In Dukhun in 1827 it was from -0150 to -1892 ; 

 in 1828 from -0155 to "1856; in 1829 from '0281 to '1648; and in 1830 from -0327 

 to "1950. The mean of the monthly variations at Bogota are from '0580 to -106211. 

 Mine for 1827 were from "0489 in July to -1616 in December; in 1828 from -0471 in 

 July to -1505 in February; in 1829 from "0654 in July to '1358 in January; and in 

 1830 from '0750 in July to -1430 in April. Considering that my observations were 

 made on a level more than 6000 feet lower than that of Messrs. Boussingault and 

 Rivero, the above data exhibit curious approximations, and prove that diurnal varia- 

 tions in the pressure of the atmosphere at great differences of level may have consi- 

 derable uniformity. But to this we find an immediate exception, for Dr. Walker at 

 Mahabuleshwur, at 4500 feet above the sea, and a few miles south of the latitude of 

 Poona, found the mean fall for ten months, from 9 — 10 a.m. to 4—5 p.m., to be '0694, 

 difference of thermometer attached +2°-61, which is infinitely less than M. Boussin- 

 gault's mean at 8000 feet. 



The monthly means of the diurnal oscillations in consecutive years, although not 

 uniform, have marked approximations. The five monsoon months in each year ex- 



* 2«''«-4 to Z^^'O. t l»°»-7 to a^'^-a. X 2'°'"-6 to 3'""'-3. § 0°>'"'63 to 3«"»-64. !l I'^'^'S to 2'»°"7. 

 MDCCCXXXV. Z 



