Books: Himalayan Journals (Complete)

J >> J. D. Hooker >> Himalayan Journals (Complete)

Pages:
1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 | 16 | 17 | 18 | 19 | 20 | 21 | 22 | 23 | 24 | 25 | 26 | 27 | 28 | 29 | 30 | 31 | 32 | 33 | 34 | 35 | 36 | 37 | 38 | 39 | 40 | 41 | 42 | 43 | 44 | 45 | 46 | 47 | 48 | 49 | 50 | 51 | 52 | 53 | 54 | 55 | 56 | 57 | 58 | 59 | 60 | 61 | 62 | 63 | 64 | 65 | 66 | 67 | 68 | 69 | 70 | 71

The diurnal distribution of temperature is equally and similarly
affected by the presence of vapour at different altitudes. The lower
and outer ranges of 6000 to 10,000 feet, first receive the diurnal
charge of vapour-loaded southerly winds; those beyond them get more
of the sun's rays, and the rearward ones more still. Though the
summer days of the northern localities are warmer than their
elevation would indicate, the nights are not proportionally cold; for
the light mist of 14,000 feet, which replaces the dense fog of 7000
feet, effectually obstructs nocturnal radiation, though it is less an
obstacle to solar radiation. Clear nights, be it observed, are as
rare at Momay (15,300 feet) as at Dorjiling, the nights if windy
being rainy; or, if calm, cold currents descend from the mountains,
condensing the moist vapours of the valleys, whose narrow floors are
at sunrise bathed in mist at all elevations in Sikkim. The rise and
dispersion of these dense mists, and their collection and
recondensation on the mountains in the morning, is one of the most
magnificent phenomena of the Himalaya, when viewed from a proper
elevation; it commences as soon as the sun appears on the horizon.

The mean daily range of the thermometer at 7000 feet is 13 degrees in
cleared spots, but considerably less in wooded, and certainly
one-third less in the forest itself. At Calcutta, which has almost an
insular climate, it amounts to 17 degrees; at Delhi, which has a
continental one, to 24.6 degrees; and in London to 17.5 degrees.
At 11,000 feet it amounts to about 20 degrees, and at 15,000 feet to
27 degrees. These values vary widely in the different months, being
much less in the summer or rainy months. The following is probably a
fair approximation:--

At 7,000 feet it amounts to 8-9 degrees in Aug. and Sept., and 17
degrees in Dec. At 11,000 feet it amounts to 12 degrees in Aug. and
Sept., and 30 degrees in Dec. At 15,000 feet it amounts to 15 degrees
in Aug. and Sept., and 40 degrees in Dec. At London it amounts to 20
degrees in Aug. and Sept., and 10 degrees in Dec.

The distribution of temperature throughout the day and year varies
less at Dorjiling than in most mountainous countries, owing to the
prevailing moisture, the effect of which is analogous to that of a
circumambient ocean to an island: the difference being, that in the
case of the island the bulk of water maintains an uniform
temperature; in that of Dorjiling the quantity of vapour acts
directly by interfering with terrestrial and solar-radiation, and
indirectly by nurturing a luxuriant vegetation. The result in the
latter case is a climate remarkable for its equability, and similar
in many features to that of New Zealand, South-west Chili, Fuegia,
and the damp west coasts of Scotland and Ireland, and other countries
exposed to moist sea winds.

The mean temperature of the year at Dorjiling, as taken by maxima and
minima thermometers* [The mean of several of the months, thus
deduced, often varies a good deal from the truth, owing to the
unequal diurnal distribution of heat; a very few minutes' sunshine
raises the temperature l0 degrees or 15 degrees above the mean of the
day; which excessive heat (usually transient) the maximum thermometer
registers, and consequently gives too high a mean.] by Dr. Chapman,
is nearly the same as that of March and October: January, the coldest
month, is more than 13.4 degrees colder than the mean of the year;
but the hottest month is only 8.3 degrees warmer than the same mean:
at Calcutta the months vary less from the mean; at Delhi more; and in
London the distribution is wholly different; there being no rains to
modify the summer heat, July is 13 degrees hotter, and January 14
degrees colder than the mean of the year.

This distribution of the seasons has a most important effect upon
vegetation, to which sufficient attention has not been paid by
cultivators of alpine Indian plants; in the first place, though
English winters are cold enough for such, the summers are too hot and
dry; and, in the second place, the great accession of temperature,
causing the buds to burst in spring, occurs in the Himalaya in March,
when the temperature at 7000 feet rises 8 degrees above that of
February, raising the radiating thermometer always above the freezing
point, whence the young leaves are never injured by night frost: in
England the corresponding rise is only 3 degrees, and there is no
such accession of temperature till May, which is 8 degrees warmer
than April; hence, the young foliage of many Himalayan plants is cut
off by night frosts in English gardens early in the season, of which
_Abies Webbiana_ is a conspicuous example.

The greatest heat of the day occurs at Dorjiling about noon, owing to
the prevalent cloud, especially during the rainy months, when the sun
shines only in the mornings, if at all, and the clouds accumulate as
the day advances. According to hourly observations of my own, it
occurred in July at noon, in August at 1 p.m., and in September (the
most rainy month) there was only four-tenths of a degree difference
between the means of noon, 1 p.m., and 2 p.m., but I must refer to
the abstracts at the end of this chapter for evidence of this, and of
the wonderful uniformity of temperature during the rainy months.
In the drier season again, after September, the greatest heat occurs
between 2 and 3 p.m.; in Calcutta the hottest hour is about 2.45
p.m., throughout the year; and in England also about 3 p.m.

The hour whose temperature coincides with the mean of the day
necessarily varies with the distribution of cloud and sunshine; it is
usually about 7 a.m. and 7 p.m.; whereas in Calcutta the same
coincidence occurs at a little before 10 a.m., and in England at
about 8 a.m.

Next to the temperature of the air, observations on that of the earth
are perhaps of the greatest value; both from their application to
horticulture, and from the approximation they afford to the mean
temperature of the week or month in which they are taken. These form
the subject of a separate chapter.

Nocturnal and solar radiation, the one causing the formation of dew
and hoar-frost when the air in the shade is above freezing, end
killing plants by the rapid abstraction of heat from all their
surfaces which are exposed to the clear sky, and the other scorching
the skin and tender plants during the day, are now familiar
phenomena, and particularly engaged my attention during my whole
Indian journey. Two phenomena particularly obstruct radiation in
Sikkim--the clouds and fog from the end of May till October, and the
haze from February till May. Two months alone are usually clear; one
before and one after the rains, when the air, though still humid, is
transparent. The haze has never been fully explained, though a
well-known phenomenon. On the plains of India, at the foot of the
hills, it begins generally in the forenoon of the cold season, with
the rise of the west wind; and, in February especially, obscures the
sun's disc by noon; frequently it lasts throughout the twenty-four
hours, and is usually accompanied by great dryness of the atmosphere.
It gradually diminishes in ascending, and have never experienced it
at 10,000 feet; at 7000, however, it very often, in April, obscures
the snowy ranges 30 miles off, which are bright and defined at
sunrise, and either pale away, or become of a lurid yellow-red,
according to the density of this haze, till they disappear at 10 a.m.
I believe it always accompanies a south-west wind (which is a
deflected current of the north-west) and dry atmosphere in Sikkim.

The observations for solar radiation were taken with a black-bulb
thermometer, and also with actinometers, but the value of the data
afforded by the latter not being fixed or comparative, I shall give
the results in a separate section. (See Appendix K.) From a multitude
of desultory observations, I conclude that at 7,400 feet, 125.7
degrees, or + 67 degrees above the temperature of the air, is the
average maximum effect of the sun's rays on a black-bulb thermometer*
[From the mean of very many observations, I find that 10 degrees is
the average difference at the level of the sea, in India, between two
similar thermometers, with spherical bulbs (half-inch diam.), the one
of black, and the other of plain glass, and both being equally
exposed to the sun's rays.] throughout the year, amounting rarely to
+ 70 degrees and + 80 degrees in the summer months, but more
frequently in the winter or spring. These results, though greatly
above what are obtained at Calcutta, are not much, if at all, above
what may be observed on the plains of India. This effect is much
increased with the elevation. At 10,000 feet in December, at 9 a.m.,
I saw the mercury mount to 132 degrees with a difl: of + 94 degrees,
whilst the temperature of shaded snow hard by was 22 degrees; at
13,100 feet, in January, at 9 a.m., it has stood at 98 degrees, diff.
+ 68.2 degrees; and at 10 a.m., at 114 degrees, diff. + 81.4 degrees,
whilst the radiating thermometer on the snow had fallen at sunrise to
0.7 degree. In December, at 13,500 feet, I have seen it 110 degrees,
diff. + 84 degrees; at 11 a.m., 11,500 feet; 122 degrees, diff: + 82
degrees. This is but a small selection from many instances of the
extraordinary power of solar radiation in the coldest months, at
great elevations.

Nocturnal and terrestrial radiation are even more difficult phenomena
for the traveller to estimate than solar radiation, the danger of
exposing instruments at night being always great in wild countries.
I most frequently used a thermometer graduated on the glass, and
placed in the focus of a parabolic reflector, and a similar one laid
upon white cotton,* [Snow radiates the most powerfully of any
substance I have tried; in one instance, at 13,000 feet, in January,
the thermometer on snow fell to 0.2 degree, which was 10.8 degrees
below the temperature at the time, the grass showing 6.7 degrees; and
on another occasion to l.2 degrees, when the air at the time (before
sunrise) was 21.2 degrees; the difference therefore being 20 degrees.
I have frequently made this observation, and always with a similar
result; it may account for the great injury plants sustain from a
thin covering of ice on their foliage, even when the temperature is
but little below the freezing-point.] and found no material
difference in the mean of many observations of each, though often 1
degree to 2 degrees in individual ones. Avoiding radiation from
surrounding objects is very difficult, especially in wooded
countries. I have also tried the radiating power of grass and the
earth; the temperature of the latter is generally less, and that of
the former greater, than the thermometer exposed on cotton or in the
reflector, but much depends on the surface of the herbage and soil.

The power of terrestrial, like that of solar radiation, increases
with the elevation, but not in an equal proportion. At 7,400 feet,
the mean of all my observations shows a temperature of 35.4 degrees.
During the rains, 3 degrees to 4 degrees is the mean maximum, but the
nights being almost invariably cloudy, it is scarcely on one night
out of six that there is any radiation. From October to December the
amount is greater = 10 degrees to 12, and from January till May
greater still, being as much as 15 degrees. During the winter months
the effect of radiation is often felt throughout the clear days, dew
forming abundantly at 4000 to 8000 feet in the shaded bottoms of
narrow valleys, into which the sun does not penetrate till 10 a.m.,
and from which it disappears at 3 p.m. I have seen the thermometer in
the reflector fall 12 degrees at 10 a.m. in a shaded valley.
This often produces an anomalous effect, causing the temperature in
the shade to fall after sunrise; for the mists which condense in the
bottom of the valleys after midnight disperse after sunrise, but long
before reached by the sun, and powerful radiation ensues, lowering
the surrounding temperature: a fall of 1 degree to 2 degrees after
sunrise of air in the shade is hence common in valleys in November
and December.* [Such is the explanation which I have offered of this
phenomenon in the Hort. Soc. Journal. On thinking over the matter
since, I have speculated upon the probability of this fall of
temperature being due to the absorption of heat that must become
latent on the dispersion of the dense masses of white fog that choke
the valleys at sunrise.] The excessive radiation of the winter months
often gives rise to a curious phenomenon; it causes the formation of
copious dew on the blanket of the traveller's bed, which radiates
heat to the tent roof, and this inside either an open or a closed
tent. I have experienced this at various elevations, from 6000 to
16,000 feet. Whether the minimum temperature be as high as 50
degrees, or but little above zero, the effect is the same, except
that hoar-frost or ice forms in the latter case. Another remarkable
effect of nocturnal radiation is the curl of the alpine rhododendron
leaves in November, which is probably due to the freezing and
consequent expansion of the water in the upper strata of cells
exposed to the sky. The first curl is generally repaired by the
ensuing day's sun, but after two or three nights the leaves become
permanently curled, and remain so till they fall in the following
spring.

I have said that the nocturnal radiation in the English spring months
is the great obstacle to the cultivation of many Himalayan plants;
but it is not therefore to be inferred that there is no similar
amount of radiation in the Himalaya; for, on the contrary, in April
its amount is much greater than in England, frequently equalling 13
degrees of difference; and I have seen 16 degrees at 7,500 feet; but
the minimum temperature at the time is 51 degrees, and the absolute
amount of cold therefore immaterial. The mean minimum of London is 38
degrees, and, when lowered 5.5 degrees by radiation, the consequent
cold is very considerable. Mr. Daniell, in his admirable essay on the
climate of London, mentions 17 degrees as the maximum effect of
nocturnal radiation ever observed by him. I have registered 16
degrees in April at Dorjiling; nearly as much at 6000 feet in
February; twice 13 degrees, and once 14.2 degrees in September at
15,500 feet; and 10 degrees in October at 16,800 feet; nearly 13
degrees in January at 7000 feet; 14.5 degrees in February at that
elevation, and, on several occasions, 14.7 degrees at 10,000 feet in
November.

The annual rain-fall at Dorjiling averages 120 inches (or 10 feet),
but varies from 100 to 130 in different years; this is fully three
times the amount of the average English fall,* [The general ideas on
the subject of the English rain-fall are so very vague, that I may be
pardoned for reminding my readers that in 1852, the year of
extraordinary rain, the amounts varied from 28.5 inches in Essex, to
50 inches at Cirencester, and 67.5 (average of five years) at
Plympton St. Mary's, and 102.5 at Holme, on the Dart.] and yet not
one-fourth of what is experienced on the Khasia hills in Eastern
Bengal, where fifty feet of rain falls. The greater proportion
descends between June and September, as much as thirty inches
sometimes falling in one month. From November to February inclusive,
the months are comparatively dry; March and October are characterised
by violent storms at the equinoxes, with thunder, destructive
lightning, and hail.

The rain-gauge takes no account of the enormous deposition from mists
and fogs: these keep the atmosphere in a state of moisture, the
amount of which I have estimated at 0.88 as the saturation-point at
Dorjiling, 0.83 being that of London. In July, the dampest month, the
saturation-point is 0.97; and in December, owing to the dryness of
the air on the neighbouring plains of India, whence dry blasts pass
over Sikkim, the mean saturation-point of the month sometimes falls
as low as 0.69.

The dew-point is on the average of the year 49.3 degrees, or 3
degrees below the mean temperature of the air. In the dampest month
(July) the mean dew-point is only eight-tenths of a degree below the
temperature, whilst in December it sinks 10 degrees below it.
In London the dew-point is on the average 5.6 degrees below the
temperature; none of the English months are so wet as those of
Sikkim, but none are so dry as the Sikkim December sometimes is.

_On the weight of the atmosphere in Sikkim; and its effects on the
human frame._

Of all the phenomena of climate, the weight of the atmosphere is the
most remarkable for its elusion of direct observation, when unaided
by instruments. At the level of the sea, a man of ordinary bulk and
stature is pressed upon by a auperincumbent weight of 30,000 pounds
or 13.5 tons. An inch fall or rise in the barometer shows that this
load is lightened or increased, sometimes in a few hours, by nearly
1,000 pounds; and no notice is taken of it, except by the
meteorologist, or by the speculative physician, seeking the subtle
causes of epidemic and endemic domplaints. At Dorjiling (7,400 feet),
this load is reduced to less than 2,500 pounds, with no appreciable
result whatever on the frame, however suddenly it be transported to
that elevation. And the observation of my own habits convinced me
that I took the same amount of meat, drink, sleep, exercise and work,
not only without inconvenience, but without the slightest perception
of my altered circumstances. On ascending to 14,000 feet, owing to
the diminished supply of oxygen, exercise brings on vertigo and
headache; ascending higher still, lassitude and tension across the
forehead ensue, with retching, and a sense of weight dragging down
the stomach, probably due to dilatation of the air contained in that
organ. Such are the all but invariable effects of high elevations;
varying with most persons according to the suddenness and steepness
of the ascent, the amount and duration of exertion, and the length of
time previously passed at great heights. After having lived for some
weeks at 15,300 feet, I have thence ascended several times to 18,500,
and once above 19,000 feet, without any sensations but lassitude and
quickness of pulse;* [I have in a note to vol. ii. chapter xxiii,
stated that I never experienced in my own person, nor saw in others,
bleeding at the ears, nose, lips, or eyelids.] but in these instances
it required great caution to avoid painful symptoms. Residing at
15,300 feet, however, my functions were wholly undisturbed; nor could
I detect any quickness of pulse or of respiration when the body was
at rest, below 17,000 feet. At that elevation, after resting a party
of eight men for an hour, the average of their and my pulses was
above 100 degrees, both before and after eating; in one case it was
120 degrees, in none below 80 degrees.

Not only is the frame of a transient visitor unaffected (when at
rest) by the pressure being reduced from 30,000 to 13,000 pounds, but
the Tibetan, born and constantly residing at upwards of 14,000 feet,
differs in no respect that can be attributed to diminished pressure,
from the native of the level of the sea. The averaged duration of
life, and the amount of food and exercise is the same; eighty years
are rarely reached by either. The Tibetan too, however inured to cold
and great elevations, still suffers when he crosses passes 18,000 or
19,000 feet high, and apparently neither more nor less than I did.

Liebig remarks (in his "Animal Chemistry") that in an equal number of
respirations,* [For the following note I am indebted to my friend, C.
Muller, Esq., of Patna.--

According to Sir H. Davy, a man consumes 45,504 cubic inches of
oxygen in twenty-four hours, necessitating the inspiration of 147,520
cubic inches of atmospheric air.--At pressure 23 inches, and temp. 60
degrees this volume of atmospheric air (dry) would weigh 35,138•75
grains.-At pressure 30 in., temp. 80°, it would weigh 43,997.83 gr.

The amount of oxygen in atmospheric air is 23.32 per cent. by weight.
The oxygen, then, in 147,520 cubic inches of dry air, at pressure 23
in., temp. 80 degrees, weighs 8,194.35 gr.; and at pressure 30 in.,
temp. 80 degrees, it weighs 10,260.25 gr.

Hence the absolute quantity of oxygen in a given volume of
atmospheric air, when the pressure is 23 in., and the temp. 60
degrees, is 20.14 per cent. less than when the pressure is 30 in. and
the temp. 80 degrees.

When the air at pressure 23 in:, temp. 60 degrees, is saturated with
moisture, the proportion of dry air and aqueous vapour in 100 cubic
inches is as follows:--
Dry air 97.173
Vapour 2.827
At pressure 30 in., temp. 80 degrees, the proportions are:--
Dry air 96.133
Vapour 3.867

The effect of aqueous vapour in the sir on the amount of oxygen
available for consumption, is very trifling; and it must not be
forgotten that aqueous vapour supplies oxygen to the system as well
as atmospheric air.] we consume a larger amount of oxygen at the
level of the sea than on a mountain; and it can be shown that under
ordinary circumstances at Dorjiling, 20.14 per cent. less is inhaled
than on the plains of India. Yet the chest cannot expand so as to
inspire more at once, nor is the respiration appreciably quickened;
by either of which means nature would be enabled to make up the
deficiency. It is true that it is difficult to count one's own
respirations, but the average is considered in a healthy man to be
eighteen in a minute; in my own case it is sixteen, an acceleration
of which by three or four could not have been overlooked, in the
repeated trials I made at Dorjiling, and still less the eight
additional inhalations required at 15,000 feet to make up for the
deficiency of oxygen in the air of that elevation.

It has long been surmised that an alpine vegetation may owe some of
its peculiarities to the diminished atmospheric pressure; and that
the latter being a condition which the gardener cannot supply, he can
never successfully cultivate such plants in general. I know of no
foundation for this hypothesis; many plants, natives of the level of
the sea in other parts of the world, and some even of the hot plains
of Bengal, ascend to 12,000 and even 15,000 feet on the Himalaya,
unaffected by the diminished pressure. Any number of species from low
countries may be cultivated, and some have been for ages, at 10,000
to 14,000 feet without change. It is the same with the lower animals;
innumerable instances may with ease be adduced of pressure alone
inducing no appreciable change, whilst there is absence of proof to
the contrary. The phenomena that accompany diminished pressure are
the real obstacles to the cultivation of alpine plants, of which cold
and the excessive climate are perhaps the most formidable.
Plants that grow in localities marked by sudden extremes of heat and
cold, are always very variable in stature, habit, and foliage. In a
state of nature we say the plants "accommodate themselves" to these
changes, and so they do within certain limits; but for one that
survives of all the seeds that germinate in these inhospitable
localities, thousands die. In our gardens we can neither imitate the
conditions of an alpine climate, nor offer others suited to the
plants of such climates.

The mean height of the barometer at Mr. Hodgson's was 23.010, but
varied 0.161 between July, when it was lowest, and October, when it
was highest; following the monthly rise and fall of Calcutta as to
period, but not as to amount (or amplitude); for the mercury at
Calcutta stands in July upwards of half an inch (0.555 Prinsep) lower
than it does in December.

The diurnal tide of atmosphere is as constant as to the time of its
ebb and flow at Dorjiling as at Calcutta; and a number of very
careful observations (made with special reference to this object)
between the level of the plains of India, and 17,000 feet, would
indicate that there is no very material deviation from this at any
elevation in Sikkim. These times are very nearly 9.50 a.m. and about
10 p.m. for the maxima, the 9.50 a.m. very constantly, and the 10
p.m. with more uncertainty; and 4 a.m. and 4 p.m. for the minima, the
afternoon ebb being most true to its time, except during the rains.

At 9.50 a.m. the barometer is at its highest, and falls till 4 p.m.,
when it stands on the average of the year 0.074 of an inch lower;
during the same period the Calcutta fall is upwards of one-tenth of
an inch (0.121 Prinsep).

It has been proved that at considerable elevations in Europe, the
hours of periodic ebb and flow differ materially from those which
prevail at the level of the sea; but this is certainly not the case
in the Sikkim Himalaya.

The amplitude decreases in amount from 0.100 at the foot of the
hills, to 0.074 at 7,000 feet; and the mean of 132 selected
unexceptionable observations, taken at nine stations between 8000 and
15,500 feet, at 9.50 a.m. and 4 p.m., gives an average fall of 0.056
of an inch; a result which is confirmed by interpolation from
numerous horary observations at these and many other elevations,
where I could observe at the critical hours.