Himalayan Journals Part 56

Month February Upper Stations Jillapahar, 7,430 feet Lower Stations Guard-house, Great Rungeet, 1,864 feet 1 degree= 298 feet

Month April Upper Stations Leebong, 6000 feet Lower Stations Guard-house, Great Rungeet, 1,864 feet 1 degree= 297 feet

Month April Upper Stations Jillapahar, 7,430 feet Lower Stations Khersiong, 4,813 feet 1 degree= 297 feet

Month March and April Upper Stations Khersiong, 4,813 feet Lower Stations Punkabaree, 1,850 feet 1 degree= 223 feet

Month March, April, May Upper Stations Jillapahar, 7,430 feet Lower Stations Punkabaree, 1,850 feet 1 degree= 253 feet

Mean 1 degree=273 feet

The above results would seem to indicate that up to an elevation of 7,500 feet, the temperature diminishes rather more than 1 degree Fahr. for every 300 feet of ascent or thereabouts; that this decrement is much leas in the summer than in the winter months; and I may add that it is less by day than by night. There is much discrepancy between the results obtained at greater or less elevations than 7000 feet; but a careful study of these, which I have arranged in every possible way, leads me to the conclusion that the proportion map be roughly indicated thus:--

1 degree=300 feet, for elevations from 1000 to 8000 feet.

1 degree=320 feet, for elevations from 8000 to 10,000 feet.

1 degree=350 feet, for elevations from 10,000 to 14,000 feet.

1 degree=400 feet, for elevations from 14,000 to 18,000 feet.

VIII.--_Khasia mountain observations._

Churra Poonji Date June 13 to 26 Calcutta Observations 86.3 degrees Number of Observations 63 Churra Observations 70.1 degrees Number of Observations 67 1 degree= 300 feet Alt.i.tude above the Sea 4,069 feet

Date August 7 to September 4 Calcutta Observations 84.6 degrees Number of Observations 196 Churra Observations 69.2 degrees Number of Observations 214 1 degree= 331 feet Alt.i.tude above the Sea 4,225 feet

Date October 29 to November 16 Calcutta Observations 80.7 degrees Number of Observations 85 Churra Observations 63.1 degrees Number of Observations 133 1 degree= 282 feet Alt.i.tude above the Sea 4,225 feet

Total Calcutta Observations 354 Total Churra Observations 414 Mean 1 degree= 304 feet

Kala-panee Date June, Aug., Sept.

Calcutta Observations 85.5 degrees Number of Observations 35 Khasia Observations 67.4 degrees Number of Observations 35 1 degree= 345 feet Alt.i.tude above the Sea 5,302 feet

Moflong Date June, July, Aug., Oct.

Calcutta Observations 85.9 degrees Number of Observations 73 Khasia Observations 68.8 degrees Number of Observations 74 1 degree= 373 feet Alt.i.tude above the Sea 6,062 feet

Syong Date Calcutta Observations 85.1 degrees Number of Observations 4 Khasia Observations 65.0 degrees Number of Observations 6 1 degree= 332 feet Alt.i.tude above the Sea 5,734 feet

Myrung Date August Calcutta Observations 89.1 degrees Number of Observations 42 Khasia Observations 69.7 degrees Number of Observations 41 1 degree= 343 feet Alt.i.tude above the Sea 5,632 feet

Myrung Date October Calcutta Observations 82.9 degrees Number of Observations 21 Khasia Observations 63.2 degrees Number of Observations 58 1 degree= 336 feet Alt.i.tude above the Sea 5,632 feet

Nunklow Calcutta Observations 86.4 degrees Number of Observations 139 Khasia Observations 70.9 degrees Number of Observations 139 1 degree= 372 feet Alt.i.tude above the Sea 4,688 feet

Mooshye Date September 23 Calcutta Observations 78.5 degrees Number of Observations 9 Khasia Observations 66.3 degrees Number of Observations 12 1 degree= 499 feet Alt.i.tude above the Sea 4,863 feet

Pomrang Date September 23 Calcutta Observations 82.7 degrees Number of Observations 51 Khasia Observations 65.8 degrees Number of Observations 51 1 degree= 369 feet Alt.i.tude above the Sea 5,143 feet

Amwee Date September 23 Calcutta Observations 79.9 degrees Number of Observations 15 Khasia Observations 67.1 degrees Number of Observations 11 1 degree= 396 feet Alt.i.tude above the Sea 4,105 feet

Joowy Date September 23 Calcutta Observations 79.5 degrees Number of Observations 11 Khasia Observations 69.0 degrees Number of Observations 7 1 degree= 567 feet Alt.i.tude above the Sea 4,387 feet

Total Calcutta Observations 400 Total Khasia Observations 434 Mean 1 degree= 385 feet

The equivalent thus deduced is far greater than that brought out by the Sikkim observations. It indicates a considerably higher temperature of the atmosphere, and is probably attributable to the evolution of heat during extraordinary rain-fall, and to the formation of the surface, which is a very undulating table-land, and everywhere traversed by broad deep valleys, with very steep, often precipitous flanks; these get heated by the powerful sun, and from them, powerful currents ascend. The scanty covering of herbage too over a great amount of the surface, and the consequent radiation of heat from the earth, must have a sensible influence on the mean temperature of the summer months.

APPENDIX J.

ON THE MEASUREMENT OF ALt.i.tUDES BY THE BOILING-POINT THERMOMETER.

The use of the boiling-point thermometer for the determination of elevations in mountainous countries appearing to me to be much underrated, I have collected the observations which I was enabled to take, and compared their results with barometrical ones.

I had always three boiling-point thermometers in use, and for several months five; the instruments were constructed by Newman, Dollond, Troughton, and Simms, and Jones, and though all in one sense good instruments, differed much from one another, and from the truth.

Mr. Welsh has had the kindness to compare the three best instruments with the standards at the Kew Observatory at various temperatures between 180 degrees and the boiling-point; from which comparison it appears, that an error of l.5 degrees may be found at some parts of the scale of instruments most confidently vouched for by admirable makers. Dollond's thermometer, which Dr. Thomson had used throughout his extensive west Tibetan journeys, deviated but little from the truth at all ordinary temperatures. All were so far good, that the errors, which were almost entirely attributable to carelessness in the adjustments, were constant, or increased at a constant ratio throughout all parts of the scale; so that the results of the different instruments have, after correction, proved strictly comparable.

The kettle used was a copper one, supplied by Newman, with free escape for the steam; it answered perfectly for all but very high elevations indeed, where, from the water boiling at very low temperatures, the metal of the kettle, and consequently of the thermometer, often got heated above the temperature of the boiling water.

I found that no confidence could be placed in observations taken at great elevations, by plunging the thermometer in open vessels of boiling water, however large or deep, the abstraction of heat from the surface being so rapid, that the water, though boiling below, and hence bubbling above, is not uniformly of the same temperature throughout.

In the Himalaya I invariably used distilled, or snow or rain-water; but often as I have tried common river-water for comparison, I never found that it made any difference in the temperature of the boiling-point. Even the mineral-spring water at Yeumtong, and the detritus-charged glacial streams, gave no difference, and I am hence satisfied that no objection can be urged against river waters of ordinary purity.

On several occasions I found anomalous rises and falls in the column of mercury, for which I could not account, except theoretically, by a.s.suming breaks in the column, which I failed to detect on lifting the instrument out of the water; at other times, I observed that the column remained for several minutes stationary, below the true temperature of the boiling water, and then suddenly rose to it.

These are no doubt instrumental defects, which I only mention as being sources of error against which the observer must be on the watch: they can only be guarded against by the use of two instruments.

With regard to the formula employed for deducing the alt.i.tude from a boiling-point observation, the same corrections are to a great extent necessary as with barometric observations: if no account is taken of the probable state of atmospheric pressure at the level of the sea at or near the place of observation, for the hour of the day and month of the year, or for the lat.i.tude, it is obvious that errors of 600 to 1000 feet may be acc.u.mulated. I have elsewhere stated that the pressure at Calcutta varies nearly one inch (1000 feet), between July and January; that the daily tide amounts to one-tenth of an inch (=100 feet); that the multiplier for temperature is too great in the hot season and too small in the cold; and I have experimentally proved that more accuracy is to be obtained in measuring heights in Sikkim, by a.s.suming the observed Calcutta pressure and temperature to accord with that of the level of the sea in the lat.i.tude of Sikkim, than by employing a theoretical pressure and temperature for the lower station.

In the following observations, the tables I used were those printed by Lieutenant-Colonel Boileau for the East India Company's Magnetic Observatory at Simla, which are based upon Regnault's Table of the 'Elastic Force of Vapour.' The mean height of the barometrical column is a.s.sumed (from Bessel's formula) to be 29.924 at temp. 32 degrees, in lat. 45 degrees, which, differing only .002 from the barometric height corresponding to 212 degrees Fahrenheit, as determined experimentally by Regnault, gives 29.921 as the pressure corresponding to 212 degrees at the level of the sea.

The approximate height in feet corresponding to each degree of the boiling-point, is derived from Oltmann's tables. The multipliers for the mean temperature of the strata of atmosphere pa.s.sed through, are computed for every degree Fahrenheit, by the formula for expansion usually employed, and given in Baily's Astronomical Tables and Biot's Astronomie Physique.

For practical purposes it may be a.s.sumed that the traveller, in countries where boiling-point observations are most desired, has never the advantage of a contemporaneous boiling-point observation at a lower station. The approximate difference in height is hence, in most cases, deduced from the a.s.sumption, that the boiling-point temperature at the level of the sea, at the place of observation, is 212 degrees, and that the corresponding temperature of the air at the level of 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 a.s.sume 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 a.s.sumption 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 mult.i.tude 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 antic.i.p.ated.

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 ma.s.ses, 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 gla.s.s 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 repet.i.tion 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 a.s.sumption 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 const.i.tutional 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.