416 CLIMATE OF SIKK1M. Appendix F. 



The diurnal tide of atmosphere is as constant as to the time of its 

 ebb and now at Dorjiling as at Calcutta ; and a number of very 

 careful observations (made with special reference to this object) 

 between the level of the plains of India, and 17,000 feet, would 

 indicate that there is no very material deviation from this at any 

 elevation in Sikkim. These times are very nearly 9*50 a.m. and about 

 10 p.m. for the maxima, the 9*50 a.m. very constantly, and the 10 p.m. 

 with more uncertainty; and 4 a.m. and 4 p.m. for the minima, the after- 

 noon ebb being most true to its time, except during the rains. 



At 9° 50 a.m. the barometer is at its highest, and falls till 4 p.m., 

 when it stands on the average of the year 0074 of an inch lower ; 

 during the same period the Calcutta fall is upwards of one-tenth of 

 an inch (0*121 Prinsep). 



It has been proved that at considerable elevations in Europe, the 

 hours of periodic ebb and flow differ materially from those which 

 prevail at the level of the sea ; but this is certainly not the case in 

 the Sikkim Himalaya. 



The amplitude decreases in amount from 0*100 at the foot of the 

 hills, to 0074 at 7,000 feet ; and the mean of 132 selected unex- 

 ceptionable observations, taken at nine stations between 8,000 and 

 15,500 feet, at 9° 50 a.m. and 4 p.m., gives an average fall of 0*056 

 of an inch ; a result which is confirmed by interpolation from nume- 

 rous horary observations at these and many other elevations, where 

 I could observe at the critical hours. 



That the Calcutta amplitude is not exceptionally great, is shewn 

 by the register kept at different places in the Grangetic valley and 

 plains of India, between Saharunpore and the Bay of Bengal. I have 

 seen apparently trustworthy records of seven * such, and find that 

 in all it amounts to between 0*084 and 0*120 inch, the "mean of the 

 whole being 0*101 of an inch. 



The amplitude is greatest (0*088) in the spring months (March, 

 April, and May), both at Dorjiling and Calcutta: it is least at 

 both in June and July, (0027 at Dorjiling), and rises again in 

 autumn (to *082 in September). 



The horary oscillations also are as remarkably uniform at all 



* Calcutta, Berampore, Benares, Nagpore, Moozufferpore, Delhi, and Saha- 

 runpore. 



