OBSERVATIONS ON THE 



night temperature was 13° on the 23rd September, had a sufficient angle to 

 approximate their altitude to twenty-five thousand feet, and this not in a 

 few detached points but a continuous line of peaks, while the paler snows 

 which encircled the summits of the most distant, indicated them to be 

 still loftier, and without assigning them the extreme height, (in that of 



assign two hundred feet for the maximum limit of error in the greatest altitudes, and at the most 

 remote distances from the site of cotemporary observations, a quantity not so great as results 

 between separate Geometric operations by the same person or between different observers, and even 

 •less than the difference in the computations of separate individuals from the same premises, and infi- 

 nitely less than the limits within which refraction varies in the ordinary state of the air. An appli- 

 cation of the argument is found in the Chur, an insulated mountain ridge, twelve thousand one hun- 

 dred and forty-seven feet high, in the hill state of Tirmw; north of Ndhn and Sahdrdnpur, chosen 

 as the grand Trigonometrical station for the survey of the country between the rivers Satlej and 

 Jamna, and its altitude fixed by a series of simultaneous observations made under different circum- 

 stances of seasons and temperature upon its summit, and Sahdrdnpur upon the plain at an oblique 

 distance of about fifty mites. This being an accessible spot, all the angles of the triangulation 

 were observed and the amount of refraction determined, the greatest accuracy is therefore due to 

 the operations. Several years after, I visited the spot on the day of the summer solstice, at the com- 

 mencement of the rainy season, when the difference of temperature between the peak and the plains 

 was about fifty Thermometrical degrees and the atmosphere variable. The Barometers I used were 

 constructed by myself upon the spot. The tubes, though under twenty-eight inches, exhibited a per- 

 fect vacuum, the mercury having been boiled within them. The scale was a fir rod, the horary obser- 

 vations were made at my camp seventy feet below the summit, and several were taken upon the 

 extreme point of the peak, the result of the whole as calculated from simultaneous observations at 

 Subathu the height of which was fixed, came within three feet of that deduced by the most accurate 

 operations of trigonometry which is perhaps proving too much. A subsequent measurement, at an 

 interval of some years, and computed from Barometrical observations at Calcutta, was within a few 

 feet of the same result. The uniformity in Barometrical indications proves their accuracy. Far 

 loftier spots than the Chur have been visited at different seasons of the year, and with different 

 Barometers with the most satisfactory results. The passes in the Himalaya at fifteen and sixteen 

 thousand feet, in the midst of eternal snow. Those upon the verge of the table land at elevations 

 of eighteen thousand feet, in a bleak arid country, and stations upon Parkyul at nineteen thousand 

 five hundred feet, and the difference in the respective heights seldom approached to one hundred 

 feet, though the temperature under which the observations were made sometimes varied forty degrees. 

 Upon every consideration then, the Barometrical levels taken in my journey to the skirts of Laddk, 

 and at various times upon the frontier of the Chinese territories, may be depended upon as true 

 indications, though I have not attempted to reduce them to measurement, but contented myself 

 with general conclusions, in round numbers, as more consistent with the nature of the subject. 



