At elevations below 4000 feet, elevations calculated from the boiling-point are not to be depended on; and Dr. Thomson remarked the same in north-west India: above 17,000 feet also the observations are hazardous, except good shelter and a very steady fire is obtainable, owing to the heating of the metal above that of the water. At all other elevations a mean error of 100 feet is on the average what is to be expected in ordinary cases. For the elevation of great mountain masses, and continuously elevated areas, I conceive that the results are as good as barometrical ones; for the general purposes of botanical geography, the boiling-point thermometer supersedes the barometer in point of practical utility, for under every advantage, the transport of a glass tube full of mercury, nearly three feet long, and cased in metal, is a great drawback to the unrestrained motion of the traveller.
In the Khasia mountains I found, from the mean of twelve stations and twenty-three observations, the multiplier as derived from the mean of the temperature at the upper station and at Calcutta, to be 75.2 degrees, and as deduced from the formula to be 73.1 degrees. Here, however, the equivalent in feet for 1 degree temp. is in summer very high, being 1 degree=385 feet. (See Appendix I.) The mean of all the elevations worked by the boiling-point is upwards of 140 feet below those worked by the barometer.
The following observations are selected as having at the time been considered trustworthy, owing to the care with which they were taken, their repetition in several cases, and the presumed accuracy of the barometrical or trigonometrical elevation with which they are compared. A small correction for the humidity of the air might have been introduced with advantage, but as in most barometrical observations, the calculations proceed on the assumption that the column of air is in a mean state of saturation; as the climate of the upper station was always very moist, and as most of the observations were taken during the rains, this correction would be always additive, and would never exceed sixty feet.
It must be borne in mind that the comparative results given below afford by no means a fair idea of the accuracy to be obtained by the boiling-point. Some of the differences in elevation are probably due to the barometer. In other cases I may have read off the scale wrong, for however simple it seems to read off an instrument, those practically acquainted with their use know well how some errors almost become chronic, how with a certain familiar instrument the chance of error is very great at one particular part of the scale, and how confusing it is to read off through steam alternately from several instruments whose scales are of different dimensions, are differently divided, and differently lettered; such causes of error are constitutional in individual observers. Again, these observations are selected without any reference to other considerations but what I have stated above; the worst have been put in with the best. Had I been dependent on the boiling-point for determining my elevations, I should have observed it oftener, or at stated periods whenever in camp, worked the greater elevations from the intermediate ones, as well as from Calcutta, and resorted to every system of interpolation. Even the following observations would be amended considerably were I to have deduced the elevation by observations of the boiling-point at my camp, and added the height of my camp, either from the boiling-point observations there, or by barometer, but I thought it better to select the most independent method of observation, and to make the level of the sea at Calcutta the only datum for a lower station.
SERIES I.—Sikkim Observations.
Elev. by
Barom. or Temp. Elev.
Place. Month. Trigonom. B.P. Air by B.P. Error
(feet) (feet) (feet)
————————————————————————————————————
Great Rungeet river Feb. B 818 210.7 56.3 904 + 86
Bhomsong Dec. 1,544 210.2 58.0 1,321 -223
Guard House, Gt Rungeet April 1,864 208.1 72.7 2,049 +185
Choongtam Aug. 5,268 202.6 65.0 5,175 - 93
Dengha Aug. 6,368 200.6 68.0 6,246 -122
Mr. Muller's (Dorjiling) Feb. Tr 6,925 199.4 41.3 7,122 +197
Dr. Campbell's (do.) April 6,932 200.1 59.5 6,745 -187
Mr. Hodgson's (do.) Feb. B 7,429 199.4 47.6 7,318 -111
Sinchul Jan. Tr 8,607 197.0 41.7 8,529 - 78
Lachoong Aug. B 8,712 196.4 54.6 8,777 + 65
Lamteng Aug. 8,884 196.3 77.0 8,937 + 53
Zemu Samdong July 8,976 196.1 58.6 8,916 - 60
Mainom Dec. Tr 10,702 193.4 38.0 10,516 -186
Junct. of Zemu & Thlonok July B 10,846 193.6 52.0 10,872 + 26
Tallum July 11,482 191.8 54.6 11,451 - 31
Yeumtong Sept. 11,919 191.3 52.2 11,887 - 32
Zemu river June 12,070 190.4 48.5 12,139 + 69
Tungu July & 12,751 189.7 43.4 12,696 - 55
Oct.
Jongri Jan. 13,194 188.8 26.0 13,151 - 43
Zemu river June 13,281 188.5 47.0 13,360 + 79
Lachee-pia Aug. 15,262 186.0 42.8 14,912 -350
Momay Sept. 15,362 186.1 48.6 14,960 -402
Palung Oct. 15,620 185.4 45.8 15,437 -183
Kongra Lama July 15,694 184.1 41.5 16,041 +347
Snow-bed above Yeumtong Sept. 15,985 184.6 44.5 15,816 -169
Tunkra pass Aug. 16,083 164.1 39.0 16,137 + 54
Yeumtso Oct. 16,808 183.1 15.0 16,279 -529
Donkia Sept. 16,978 182.4 41.0 17,049 + 71
Mountain above Momay Sept. 17,394 181.9 47.8 17,470 + 76
Sebolah pass Sept. 17,585 181.9 46.5 17,517 - 68
Kinchinjhow Sept. 17,624 181.0 47.5 18,026 +402
Donkia Mountain Sept. 18,510 180.6 37.1 18,143 -367
Ditto Sept. 18,307 179.9 38.8 18,597 +290
Bhomtso Oct. 18,450 181.2 52.0 18,305 -145
Donkia pass Sept. 18,466 181.2 45.5 17,866 -600
————————————————————————————————————
Mean - 58
SERIES II.—Khasia Mountains.
Elev. Elev.
Place Month Bar. B.P. Tm. Air by B.P. Diff.
(feet) (feet) (feet)
———————————————————————————————————
Churra June 4,069 204.4 70.3 4,036 - 33
Amwee Sept. 4,105 205.1 67.7 4,041 - 64
Nurtiung Oct. 4,178 205.0 70.0 4,071 -107
Nunklow July 4,688 203.9 69.8 4,333 -355
Kala-panee June, July, 5,302 202.2 65.8 5,202 -100
Sept., Oct.
Myrung July 5,647 201.9 69.4 5,559 - 88
Syong July 5,725 201.8 70.8 5,632 - 93
Moflong July, Aug., 6,062 201.4 64.8 5,973 - 89
Oct., Nov.
Chillong Nov. 6,662 201.2 62.8 6,308 -354
———————————————————————————————————
Mean 5,160 5,016 -143