Himalayan Journals Part 43

On the dry but wooded west face of the mountain, grows _Falconeria,_ a curious Euphorbiaceous tree, with an acrid milky juice that affects the eyes when the wood is cut. Beautiful _Cycas_ palms are also common, with _Terminalia, Bignonia, Sterculia,_ dwarf _Phoenix_ palm, and Gurjun trees. The east slope of the mountain is damper, and much more densely wooded; we there found two wild species of nutmeg trees, whose wood is full of a brown acrid oil, seven palms, tree-ferns, and many other kinds of ferns, several kinds of oak, _Dracaena,_ and figs. The top is 1,136 feet above the sea, and commands an extensive view to all points of the compa.s.s; but the forests, in which the ashy bark of the Gurjun trees is conspicuous, and the beautiful valley on the west, are the only attractive features.

The weather on the east side of the range differs at this season remarkably from that on the west, where the vicinity of the sea keeps the atmosphere more humid and warm, and at the same time prevents the formation of the dense fogs that hang over the valleys to the eastward every morning at sunrise. We found the mean temperature at the bungalow, from January 9th till the 13th, to be 70.2 degrees.

We embarked again at Chittagong on the 16th of January, at 10 p.m., for Calcutta, in a very large vessel, rowed by twelve men: we made wretchedly slow progress, for the reasons mentioned earlier, being for four days within sight of Chittagong! On the 20th we only reached Sidhee, and thence made a stretch to Hattiah, an island which may be said to be moving bodily to the westward, the Megna annually cutting many acres from the east side; and the tide-wave depositing mud on the west. The surface is flat, and raised four feet above mean high-water level; the tide rises about 14 feet up the bank, and then retires for miles; the total rise and fall is, however, much less here than in the Fenny, higher up the gulf. The turf is composed of _Cynodon_ and a _Fimbristylis_; and the earth being impregnated with salt, supports different kinds of _Chenopodium._ Two kinds of tamarisk, and a th.o.r.n.y _Ca.s.sia_ and _Exoecaria,_ are the only shrubs on the eastern islands; on the central ones a few dwarf mangroves appear, with the holly-leaved _Dilivaria,_ dwarf screw-pine (_Panda.n.u.s_), a shrub of _Compositae,_ and a curious fern, a variety of _Aristichum aureum._ Towards the northern end of Hattiah, Talipot, cocoa-nut and date-palms appear.

On the 22nd we entered the Sunderbunds, rowing amongst narrow channels, where the tide rises but a few feet. The banks were covered with a luxuriant vegetation, chiefly of small trees, above which rose stately palms. On the 25th, we were overtaken by a steamer from a.s.sam, a novel sight to us, and a very strange one in these creeks, which in some places seemed hardly broad enough for it to pa.s.s through. We jumped on board in haste, leaving our boat and luggage to follow us. She had left Dacca two days before, and this being the dry season, the route to Calcutta, which is but sixty miles in a straight line, involved a detour of three hundred.

From the masts of the steamer we obtained an excellent _coup-d'oeil_ of the Sunderbunds; its swamps clothed with verdure, and intersected by innumerable inosculating channels, with banks a foot or so high.

The amount of tide, which never exceeds ten feet, diminishes in proceeding westwards into the heart of these swamps, and the epoch, direction, and duration of the ebb and flow vary so much in every ca.n.a.l, that at times, after stemming a powerful current, we found ourselves, without materially changing our course, suddenly swept along with a favouring stream. This is owing to the complex ramifications of the creeks, the flow of whose waters is materially influenced by the most trifling accidents of direction.

Receding from the Megna, the water became saltier, and _Nipa fruticans_ appeared, throwing up pale yellow-green tufts of feathery leaves, from a short thick creeping stem, and bearing at the base of the leaves its great head of nuts, of which millions were floating on the waters, and vegetating in the mud. Marks of tigers were very frequent, and the footprints of deer, wild boars, and enormous crocodiles: these reptiles were extremely common, and glided down the mud banks on the approach of the steamer, leaving between the footmarks a deep groove in the mud made by their tail. The _Phoenix paludosa,_ a dwarf slender-stemmed date-palm, from six to eight feet high, is the all-prevalent feature, covering the whole landscape with a carpet of feathery fronds of the liveliest green. The species is eminently gregarious, more so than any other Indian palm, and presents so dense a ma.s.s of foliage, that when seen from above, the stems are wholly hidden.* [_Sonneratia, Heritiera littoralis,_ and _Careya,_ form small gnarled trees on the banks, with deep s.h.i.+ning green-leaved species of _Carallia Rhizophora,_ and other Mangroves.

Occasionally the gigantic reed-mace (_Typha elephantina_) is seen, and tufts of tall reeds (_Arundo_).]

The water is very turbid, and only ten to twenty feet deep, which, we were a.s.sured by the captain, was not increased during the rains: it is loaded with vegetable matter, but the banks are always muddy, and we never saw any peat. Dense fogs prevented our progress in the morning, and we always anch.o.r.ed at dusk. We did not see a village or house in the heart of the Sunderbunds (though such do occur), but we saw canoes, with fishermen, who use the tame otter in fis.h.i.+ng; and the banks were covered with piles of firewood, stacked for the Calcutta market. As we approached the Hoogly, the water became very salt and clear; the Nipa fruits were still most abundant, floating out to sea, but no more of the plant itself was seen. As the channels became broader, sand-flats appeared, with old salt factories, and clumps of planted _Casuarina._

On the 28th of January we pa.s.sed Saugor island, and entered the Hoogly, steamed past Diamond Harbour, and landed at the Botanic Garden Ghat, where we received a hearty welcome from Dr. Falconer.

Ten days later we bade farewell to India, reaching England on the 25th of March, 1851.

APPENDIX. A.

METEOROLOGICAL OBSERVATIONS IN BEHAR, AND IN THE VALLEYS OF THE SOANE AND GANGES.

Most of the instruments which I employed were constructed by Mr.

Newman, and with considerable care: they were in general accurate, and always extremely well guarded, and put up in the most portable form, and that least likely to incur damage; they were further frequently carefully compared by myself. These are points to which too little attention is paid by makers and by travellers in selecting instruments and their cases. This remark applies particularly to portable barometers, of which I had five at various times. Although there are obvious defects in the system of adjustment, and in the method of obtaining the temperature of the mercury, I found that these instruments invariably worked well, and were less liable to derangement and fracture than any I ever used; the best proof I can give of this is that I preserved three uninjured during nearly all my excursions, left two in India, and brought a third home myself that had accompanied me almost throughout my journey.

In very dry climates these and all other barometers are apt to leak, from the contraction of the box-wood plug through which the tube pa.s.ses into the cistern. This must, in portable barometers, in very dry weather, be kept moist with a sponge. A small iron bottle of pure mercury to supply leakage should be supplied with every barometer, as also a turnscrew. The vernier plate and scale should be screwed, not soldered on the metal sheath, as if an escape occurs in the barometer-case the solder is acted upon at once. A table of corrections for capacity and capillarity should accompany every instrument, and simple directions, etc., in cases of trifling derangement, and alteration of neutral point.

The observations for temperature were taken with every precaution to avoid radiation, and the thermometers were constantly compared with a standard, and the errors allowed for. The maximum thermometer with a steel index, I found to be extremely liable to derangement and very difficult to re-adjust. Negretti's maximum thermometer was not known to me during my journey. The spirit minimum thermometers again, are easily set to rights when out of order, but in every one (of six or seven) which I took to India, by several makers, the zero point receded, the error in some increasing annually, even to-6 degrees in two years. This seems due to a vaporisation of the spirit within the tube. I have seen a thermometer of this description in India, of which the spirit seemed to have retired wholly into the bulb, and which I was a.s.sured had never been injured. In wet-bulb observations, distilled water or rain, or snow water was used, but I never found the result to differ from that obtained by any running fresh water, except such as was polluted to the taste and eye.

The hours of observation selected were at first sunrise, 9 a.m., 3 p.m., sunset, and 9 p.m., according to the instructions issued to the Antarctic expedition by the Royal Society. In Sikkim, however, I generally adopted the hours appointed at the Surveyor General's office, Calcutta; viz., sunrise, 9h. 50m. a.m., noon, 2h. 40m. p.m., 4 p.m., and sunset, to which I added a 10 p.m. observation, besides many at intermediate hours as often as possible. Of these the 9h.

50m. a.m. and 4 p.m. have been experimentally proved to be those of the maximum and minimum of atmospheric pressure at the level of the sea in India, and I did not find any great or marked deviation from this at any height to which I attained, though at 15,000 or 16,000 feet the morning maximum may occur rather earlier.

The observations for nocturnal (terrestrial) radiation were made by freely suspending thermometers with naked bulbs, or by laying them on white cotton, wool, or flannel; also by means of a thermometer placed in the focus of a silvered parabolic reflector. I did not find that the reflector possessed any decided advantage over the white cotton: the means of a number of observations taken by each approximated closely, but the difference between individual observations often amounted to 2 degrees.

Observations again indicative of the radiation from gra.s.s, whether dewed or dry, are not strictly comparable; not only does the power of radiation vary with the species, but much more with the luxuriance and length of the blades, with the situation, whether on a plane surface or raised, and with the subjacent soil. Of the great effect of the soil I had frequent instances; similar tufts of the same species of gra.s.s radiating more powerfully on the dry sandy bed of the Soane, than on the alluvium on its banks; the exposure being equal in both instances. Experiments for the surface-temperature of the soil itself, are least satisfactory of any:--adjoining localities being no less affected by the nature, than by the state of disintegration of the surface, and by the amount of vegetation in proximity to the instrument.

The power of the sun's rays in India is so considerable, and protracted through so long a period of the day, that I did not find the temperature of springs, or of running water, even of large deep rivers, so constant as was to be expected.

The temperature of the earth was taken by sinking a bra.s.s tube a yard long in the soil.

A thermometer with the bulb blackened affords the only means the traveller can generally compa.s.s, of measuring the power of the sun's rays. It should be screened or put in a blackened box, or laid on black wool.

A good Photometer being still a desideratum, I had recourse to the old wedge of coloured gla.s.s, of an uniform neutral tint, the distance between whose extremes, or between transparency and total opacity, was one foot. A moveable arm carrying a bra.s.s plate with a slit and a vernier, enables the observer to read off at the vanis.h.i.+ng point of the sun's limb, to one five-hundredth of an inch. I generally took the mean of five readings as one, and the mean of five of these again I regarded as one observation; but I place little dependence upon the results. The causes of error are quite obvious. As far as the effects of the sun's light on vegetation are concerned, I am inclined to think that it is of more importance to register the number of hours or rather of parts of each hour, that the sun s.h.i.+nes, and its clearness during the time. To secure valuable results this should be done repeatedly, and the strength of the rays by the black-bulb thermometer registered at each hour. The few actinometer observations will be found in another part of the Appendix.

The dew-point has been calculated from the wet-bulb, by Dr. Apjohn's formula, or, where the depression of the barometer is considerable, by that as modified by Colonel Boileau.* [Journal of Asiatic Society, No. 147 (1844), p.135.] The saturation-point was obtained by dividing the tension at the dew-point by that at the ordinary temperature, and the weight of vapour, by Daniell's formula.

The following summary of meteorological observations is alluded to at vol. i., chapter i.

I.--_Table-land of Birbhoom and Behar, from Taldanga to Dunwah.

Average elevation 1,135 feet._

It is evident from these observations, that compared with Calcutta, the dryness of the atmosphere is the most remarkable feature of this table-land, the temperature not being high; and to this, combined with the sterility of the soil over a great part of the surface, must be attributed the want of a vigorous vegetation. Though so favourably exposed to the influence of nocturnal radiation, the amount of the latter is small. The maximum depression of a thermometer laid on gra.s.s never exceeded 10 degrees, and averaged 7 degrees; whereas the average depression of the dew-point at the same hour amounted to 25 degrees in the morning. Of course no dew was deposited even in the clearest star-light night.

February 1848.

Hour Sunrise 9 a.m. 3 p.m. 9 p.m.

TEMPERATURE Mean 56.6 70.1 75.5 61.7 Max. 65.2 77.0 81.7 66.2 Min. 46.3 61.2 65.2 55.5 Range 18.9 15.8 16.5 10.7 WET-BULB Mean 48.2 53.7 55.3 49.3 Max. Depression 12.5 19.3 22.5 20.5 Min. Depression 6.0 14.3 16.7 9.0

Elasticity of Vapour .276 .264 .248 .248

DEW-POINT Mean 39.5 37.9 36.0 36.1 Max. 52.0 52.7 46.8 50.0 Min. 23.3 24.5 24.3 *9.1 Max. Depression 31.7 39.2 48.4 56.9 Min. Depression 10.4 24.3 34.9 16.2

Weight of Vapour in cubic feet 3.088 2.875 2.674 2.745

SATURATION Mean .550 .330 .260 .410 Max. .680 .450 .320 .590 Min. .330 .260 .190 .140

Number of observations 7 7 7 10

Extreme variations of Temperature 35.4 degrees Extreme variations of relative humidity .540 Extreme diff. Solar and Nocturnal Radiation 96.5 degrees

*Taken during a violent N.W. dust-storm.

SOLAR RADIATION

MORNING Hour Th. Black Bulb Diff. Phot.

9.30 a.m. 77.0 130 53.0 ...

10 a.m. 69.5 124 54.5 10.320 10 a.m. 77.0 137 60.0 ...

9 a.m. 63.5 94 30.5 10.230 9 a.m. 61.2 106 44.8 ...

9 a.m. 67.0 114 47.0 10.350 --------------------------------------------------- Mean 69.2 117.5 48.1 10.300

AFTERNOON Hour Th. Black Bulb Diff. Phot.

3.30 p.m. 81.7 109 27.3 ...

3 p.m. 80.5 120 39.5 10.320 3 p.m. 81.5 127 45.5 10.330 3.30 p.m. 72.7 105 32.3 10.230 3 p.m. 72.5 110 37.5 10.390 --------------------------------------------------- Mean 77.8 114.2 36.4 10.318

NOCTURNAL RADIATION

SUNRISE Exposed Th. On Earth On Gra.s.s Temperature 51.1 48.3 46.6 Mean Diff. from Air 4.0 2.5 6.2 Max. Diff. from Air 9.0 3.7 9.0 Number of Observations 6 3 5

NINE P.M.

Exposed Th. On Earth On Gra.s.s Temperature 56.4 53.8 54.4 Mean Diff. from Air 5.3 4.9 7.2 Max. Diff. from Air 7.5 5.5 10.0 Number of Observations 7 6 7

On one occasion, and that at night, the dew-point was as low as 11.5 degrees, with a temperature of 66 degrees, a depression rarely equalled at so low a temperature: this phenomenon was transient, and caused by the pa.s.sage of a current of air loaded with dust, whose particles possibly absorbed the atmospheric humidity. From a comparison of the night and morning observations of thermometers laid on gra.s.s, the earth, and freely exposed, it appears that the gra.s.s parts with its heat much more rapidly than the earth, but that still the effect of radiation is slight, lowering its temperature but 2 degrees below that of the freely exposed thermometer.

As compared with the climate of Calcutta, these hills present a remarkable contrast, considering their proximity in position and moderate elevation.