Himalayan Journals, vol 2 - J. D. Hooker (bill gates best books txt) 📗

the sea is hotter by one degree for every 330 feet of

difference in elevation. As, however, the temperature of boiling

water at the level of the sea varies at Calcutta between July and

January almost from 210.7 degrees to 212.6 degrees, I always took the Calcutta barometer observation at the day and hour of my

boiling-point observation, and corrected my approximate height by as many feet as correspond to the difference between the observed height of the barometer at Calcutta and 29.921; this correction was almost invariably (always normally) subtractive in the summer, often

amounting to upwards of 400 feet: it was additive in winter, and

towards the equinoxes it was very trifling.

For practical purposes I found it sufficient to assume the Calcutta temperature of the air at the day and hour of observation to be that of the level of the sea at the place of observation, and to take out the multiplier, from the mean of this and of the temperature at the upper station. As, however, 330 feet is a near approach to what I

have shown (Appendix I.) to be the mean equivalent of 1 degree for

all elevations between 6000 and 18,000 feet; and as the majority of my observations were taken between these elevations, it results that the mean of all the multipliers employed in Sikkim for forty-four

observations amounts to 65.1 degrees Fahrenheit, using the Calcutta and upper station observations, and 65.3 degrees on the assumption of a fall of 1 degree for every 330 feet. To show, however, how great an error may accrue in individual cases from using the formula of

1 degree to 330, I may mention that on one occasion, being at an

elevation of 12,000 feet, with a temperature of the air of 70

degrees, the error amounted to upwards of 220 feet, and as the same temperature may be recorded at much greater elevations, it follows

that in such cases the formula should not be employed without

modification.

A multitude of smaller errors, arising from anomalies in the

distribution of temperature, will be apparent on consulting my

observations on the temperature at various elevations in Sikkim;

practically these are unavoidable. I have also calculated all my

observations according to Professor J. Forbes's formula of 1 degree difference of temperature of boiling-water, being the equivalent of 550 feet at all elevations. (See Ed. Phil. Trans., vol xv. p. 405.) The formula is certainly not applicable to the Sikkim Himalaya; on

the contrary, my observations show that the formula employed for

Boileau's tables gives at all ordinary elevations so very close an

approach to accuracy on the mean of many observations, that no

material improvement in its construction is to be anticipated.

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