AND METEOROLOGY OP DUKHUN. * 175 



ninety minutes ; on the 6th it rose '008 in seventy-five minutes ; and on the 8th it 

 rose -005 in fifteen minutes ; and on the 11th of April -001 only in forty-five minutes. 



In the maximum nocturnal tide (10 — 11 p.m.) there was rarely any difference in the 

 thermometer during the oscillations of the mercury ; nevertheless the turn of the tide 

 ranged from 9^ SO'" to 1 1^ SO"*, and in two remarkable instances even beyond these 

 hours. On the 12th of October it turned at 9 p.m., and on the 9th of June at 12 p.m.; 

 both of these anomalies may have been produced by the state of the weather, there 

 having been a heavy thunder storm from 7^ to 8^ 30™ on the 9th of June, and several 

 thunder storms round the horizon on the J 2th of October, although not immediately 

 at Poona. The stationary period ranged from to 60 minutes, but of the latter there 

 is only one instance in the Table. As in the preceding tides, the movement of the 

 mercury in equal periods of time manifested occasional irregularities, although the 

 thermometer remained stationary, or nearly so. On the 6th of February the night 

 fall was '008 in 15 minutes, and on the 8th it was only -001 in 15 minutes ; in neither 

 instance was there any movement of the thermometer, whilst on the 10th of June, 

 between 10^ 45™ and 11 p.m., the barometric fall amounted to '010. From the above 

 facts, and they could be infinitely multiplied, it is clear there is not any positive uni- 

 formity in the oscillations of the mercurial column, nor in the duration of the sta- 

 tionary periods ; nevertheless as the irregularities are bounded by comparatively 

 narrow limits, the movements may be considered subject to a general law, the 

 rationale of which remains to be explained. 



Experiments have determined that the diurnal atmospheric tides (the nocturnal 

 tides have been less attended to) extend from the equator to high parallels of lati- 

 tude, but that the oscillation decreases as the latitude increases. It is further pre- 

 sumed that the oscillation gradually diminishes in ascending from the level of the sea 

 to great heights. Professor James For3es of Edinburgh has laid down an assumed 

 curve, in which the diurnal oscillation amounts to -1190 at the equator, and nil at 

 latitude 64° 8' N. ; and beyond that latitude the tide occurs with a contrary sign, 

 the maximum hour becoming the minimum. More extended and careful observations 

 in different parts of the earth will probably confirm the empirical law sought to be 

 established by Professor Forbes, but our present meteorological data offer many ex- 

 ceptions to it. In the valuable table given by Professor Forbes in his paper*, there 

 are exceptions to his law in the observations of Russell at Boorhanpoor, and Prinsep 

 at Benares, each for three years. The mean diurnal oscillation, agreeably to the 

 former, in latitude 24° 4', being less ('0877), mean temperature 75°'2, than that at 

 Benares (-1059), mean temperature 78°'8, in latitude 25° 30'. Mr. Goldingham in 

 1823, at the Madras Observatory, latitude 13° 5', observing every tenth day, found 

 the diurnal oscillation amount only to -0790, mean temperature 81°-69. At Ava in 

 the Birman empire, latitude 21° 51', agreeably to Major Burney, the oscillation 

 amounted to -1260, mean temperature 78°-39, being greater than in any other series 

 * Transactions of the Royal Society of Edinburgh, vol. xii. Part I. p, 170. 



