[[1]] *1
Dearee, West Bank of the Soane River;
Main road to Benares. Feb[ruary]. 15th 1848
My dear Prof[essor]. Wheatstone
The kindness you showed me while I was preparing my outfits for India,
encourages me to address you, when anything, which I think may be of
consequence in Physics, occurs during my travels. You are aware that Botany is
my first object; & that my observations on other branches of science must be
somewhat desultory: Still, I have been able to keep a tolerable Meteorological
Register, since leaving Calcutta *2; the results of which may be of use, as coming
from parts of the country, whose climate has never been investigated. I quitted
England, you may remember, in the 2nd week of November in HMS "Sidon" with
Lord Dalhousie & arrived in Egypt on the 4th Dec[embe]r. During our 3 days' stay
at Cairo, I made a few observations on the effects of the sun's rays on the soil, on
the depth to which the heat penetrated, & also on the power of nocturnal radiation
& thickness of soil through which the heat is radiated. In all these investigations, I
find the great difficulty to consist in choosing a position where the instrument itself
is screened from radiation. Limestone, Sand, and Sandstone-rock, in the Desert,
have all different temperatures; & except a brisk wind be stirring, they give very
different results. At the Great Pyramid I selected two stations, which I thought
unexceptionable, one at the N[orth]. face of the N[orth].E[ast]. angle, the other at
the W[est]. face of the N[orth].E[ast]. angle, & I was mortified to find as much as 5
1/2° difference in the temperature, & several in the Dew point, &c. At each angle I
shifted the Instruments from one to the other face, with the same results. At the
summit there was considerably more vapour in the atmosphere than at the base.
The temperature of the two chambers agreed (78°).
In the Desert, midway between Cairo and Suez, I found
[[2]] a little before sunrise after a very cold night, the Dewy surface to be cooled
down to 44° (Therm: in shade 47°) & the increase of the temperature to be 1° an
inch, down to 10 inches. Similar soil, on the previous & succeeding days, was
heated, (at 3 P.M.) to about 80°, & the power of the suns rays penetrated to more
than that distance.
At Suez we embarked onboard H[onorable]. E[ast]. I[ndia]. Co[mpany]. St[ea]m
Frigate, "Moozuffer" for Calcutta: & I noted three times a day the temperatures,
Dew point, &c, but not the Barometer; for my "Newman's Portable" jumped so
much as to render impossible to observe within 2/10 of an inch: this was owing to
the great power of the engines. Some of the phenomena are very curious. In the
first place, the waters of this gulf are salter than those of any other sea having a
free communication with the greater Oceans, & contain 3/10 more salt in an equal
bulk than those of the Indian Ocean. This high specific Gravity decreases on the
passage down to Mocha, where the increase is diminished to 2/10ths, & suddenly
to the usual standard of sea-water. My attention was first drawn to this by the chief
Engineer, with whom I conducted such experiments as the motion of the vessel
allowed. During Ross' voyage I had frequently examined the water (with Capt.
Ross); &, whether from the various oceans over which we passed through, or
different depths (down to 800 fathoms) in those oceans, I always obtained a very
constant quantity of salts. I also enquired about the water of the Persian Gulf, &
am assured that they do not differ from those of the Indian Ocean. From the Straits
of Babelmandel to Cape Comorin, I perceived no difference.
There are three classes of winds in the Red Sea, very remarkable in their
distribution. During all June, July, Aug & Sept. a north wind prevails throughout the
sea; produced I suppose, by the heated continents of Arabia & especially Africa; &
the same wind continues all the year round from Suez to the Straits of Jibbel,
[[3]] & with particular force down the gulf of Akabar. During the remainder of the
year the winds in the middle part of the sea, from Jibbel Teer 15° " 30" to 19° or
20° 21° North, are light and variable. In South part again from Jibbel--Teer to the
Straits: the S[outh]E[ast] wind is constant from October till May: increasing in
violence as you approach the straits. This we experienced ourselves; for we
carried N[orth]. & N[orth].E[ast]. winds from Suez to Latitude 20° variables from
Latitude 20 to Jibbel--Teer, & Suez south from Jibbel Teer to the Straits. I do not
know how far the accompanying phenomena may account for the great saltnes &
well known depression (below the level of the Mediterranean, & of the Straits
amounting if I remember aright to 35 odd feet,) of the upper part of the sea: my
observation gives the following results:
Mean
temperature
air
76 -- 1
Suez to
Lat[itude]:
20
Lat[itude]. 81 -- 6
20 -Jibbel-Teer
Jibbel
80 -- 3
Teer to
Straits
Wet bulb
D[ew].P[oint]. vapour
Thermometer
in
cub[ic].
feet
calculated
evaporation
sea
78 -- 0 68 -- 3
64 -- 1
6 -- 841 1 -- 56
80 -- 4 74 -- 5
71 -- 4
8 -- 478 1 -- 38
76 -- 0 70 -- 2
65 -- 0
4 -- 311 2 -- 61
The perennial N. wind of the upper potion, may of itself reduce the level, it is
further a drier wind & effects more evaporation from the surface, than do the winds
of the middle portion, at which it arrived loaded with vapor & increased in elasticity.
Whatever evaporation takes place at the South portion, during the dry South wind,
maybe compensated by an indraught from the Indian Ocean. The central portion
again, during the same season, receives the loaded currents from either quarter,
which its high temperature enables it to retain, its elasticity also being very
considerable.
I fear, however, that this may be a familiar subject to you but my library is limited:
the maps in the 2nd Edition of Daniell being my only guide; & there are very
inaccurate as regards the Red Sea.
[[4]] Few other phenomena of importance occurred to me during the voyage;
except a curious variety, as I suppose it, of the crepuscular arch, which I witnessed
for two nights after leaving Madras *3 Roads. The first I saw on Jan[uar]y 9th at 6
3/4 while still in view of land: it lasted hardly a minute after I first observed it &
appeared like a broad lunar rainbow, over the sun's position, & about 70° altitude.
On the following evening I looked out for it: we were then some 150 miles on our
course to Calcutta. At 3/4 hour after sunset, a pale milk--white arch, with the
faintest tinge of purple, appeared at 60° altitude. It was about 8° broad: the north
end rested on a very faint Cirrhus altitude 30°. The southend descended lower, but
did not touch the horizon: its limits were not clearly defined: it rose rapidly &
disappeared in about 3" or 5" on reaching the Zenith. The days had in both cases
been very fine & clear, the sky at the time deep blue grey, with a peach--blossom
tinge (or twilight) resting on a yellow horizon. This peach--color is a very common
tropical sunset, & for delicacy of tint unequalled. A t Aden, where it contrasted with
the stern pitchy dark crags of that Peninsular, & deep blue of the Ocean, it
produced the finest sunset effect I ever witnessed.
All this time, however, I have not told you where I am, & what doing. After a
fortnight in Calcutta, I started to join Mr Williams, who is on his way to survey a
coal--field on the Soane River, whose banks we have reached, & up which we
immediately proceed. My objects are purely Botanical; but hope, by the careful
use of good instruments, to obtain data for calculating the effects of climate on the
vegetation of large areas. We have travelled W[est]. from Burdwan, over an
elevated table--land gradually rising: its culminate point is Paris--Nath [Parasnath]
*4, the highest mountain
[[5]] in lower Bengal: this I ascended, but have no table or rule for calculating the
heights.
At the Dunwar pass, some 90 miles east, there is a rapid descent of about 800
feet, to a level plain which reaches to the Soane. We now follow up the Soane,
from whence I go to Mirzapore & return to Calcutta, for a few days, previous to
starting for Sikkim in the East Himalayah. I take observations as nearly as I can at
9 A.M., 3 P.M., 9 P.M. & between 2 A.M. & sunrise; but in the morning I cannot be
exactly punctual being often up till midnight, & always on the march long before
dawn. The barometer I observe on all occasions, "Newman's Portable" is
excellent; but I must carry it everywhere myself to be comfortable about it. When
the weather is very hot a few globules of mercury escape at the cistern.
Terrestrial radiation I observe in various way, night & morning, on the surface,
Earth, grass, leaves & at such depths as I can conveniently plunge the
Thermometer guarded with Pith. I have twice had bores made of 3 or 4 feet at
places 14' apart, & in both cases had a constant temperature of 72° for 15 hours of
afternoon and night: but this alluvium is often too hard to bore with common tools;
it always takes 6 hours & 6 men to work the jumper. I guard the bulb with pith, &
sink it in a brass tube. The dryness of the upper plains we travelled is wonderful,
during these N[orth]. W[est]. winds. I have been very careful with the wet--bulb
observations. Solar radiation is all but impracticable: I persevere in the Black bulb
& wedge of glass Photometer, made, as you recommended, by "Darker"[.]
Last night I saw the best developed aurora I ever witnessed, taking brightness,
extent of surface covered, & length of continuity of beams, into account. Never in
Scotland, where I have
[[6]] observed many, or the South Polar regions, where also these phenomena
were frequent, have I noted one, so altogether good as this. The moon spoiled it
sadly; though its beams were brilliantly defined within 8° of her orb on each side. I
send you the observations I took of it, with a good quadrant & compass, from my
first seeing it, till it had nearly disappeared at midnight. I have also transmitted an
account, to be published in Calcutta, & hope it has attracted notice elsewhere.
There is no change since in the weather, but much cirrhus since noon today, which
is unusual, though possibly owing to the hills we are now near, & which are new
features on our landscape.
Monday, Feb 14, Barroon, East bank of Soane River. 9 P.M. Bar. 29. 924. A.H.T.
68. Tp. Air 62. Wet Bulb 51.5. Grass 53. Blue sky & clear horizon. Moon & stars
clear, milky way invisible. Zodiacal light D[itt]o moon by Photometer 3.07 inch: inch:
(sun at 3 P.M. being 4.17 inches).
Observed the Auroral Arch well defined, 12° broad, altitude of upper limb (best
defined) 20°. Extremes bearing W[est]. 20 S[outh]. & N[orth]. 50 E[ast]. Light pale,
but bright, resting on an arch no darker than sky at zenith. Beams crowded, from
20--30, linear & lancet shaped, crossing the zenith & converging in opposite
horizon towards S[outh]. 15 E[ast]. All beams bright, clear, & well defined, moving
slowly, forked at the apices, or split from apex to zenith, almost obscuring stars of
1st magnitude. Longest beams point to S[outh]. 10 E[ast]. descending to 25
altitude. Middle beam broad, crosses zenith, points S[outh]. 50 E[ast]. & descends
to 40° N[orth].W[est]. beams almost parallel to horizon, point S[outh]. 70 E[ast]. &
descend to 20°[.]
10 P.M., General appearance more diffused, upper limb of arch less defined. No
beams cross the zenith. Two detached ones 15° above horizon at S[outh]. 15
E[ast].: after a few minutes one beam
[[7]] appeared on zenith.
10:15, Appearance to W[est]. of N[orth]. as before. one beam on zenith, two cross
the meridian, one to S[outh]. 30 E[ast]. at 15° above horizon, which disappears
towards the arch in S[outh]. E[ast].. Arch more diffused & descending to horizon,
forming a pale mass altitude 25°. Beams broader, shifting & splitting more
frequently. Soon a dark horizontal band 4° broad, crosses the arch, extending from
N[orth]. 55 W[est]. to N[orth]. 10 W[est].: upper limb 12° altitude: it appears as a
break in the auroral arch. Whole horizon, all round, covered with a pale diffused
light, strongest towards arch & in opposite quarter. Beams still clear; the lateral
broadest & best defined. Dark band becomes broader, breaking up the arch.
10:30. Beams from arch still clear, linear, 2°6° broad, about 12 in number; none
reach the zenith: a few lateral ones cross the moon's meridian; the upper
approaching within 8° of her orb, & still well defined. N[orth]. E[ast]. beams most
crowded: N[orth]. W[est]. best defined & broadest. Dark band broader, severing
the arch. Whole Phenomena fading: longest & brightest & most numerous beams
stretching along N[orth]. E[ast]. horizon. 10:50 still fading. Beams & arch all
disappearing to W[est]. of N[orth].: 18 narrow beams between N[orth]. & W[est]. 20
E[ast]. from remains of arch. Cold southerly breeze sprung up.
10:55. Breaking up, as before. 11 P.M. Diffused light over all horizon, (possibly
reflection of the moon's light on ground mist, which, however, is not discernible).
Scattered beams like cirrhus here & there: linear along the N[orth]. & N[orth].
E[ast]. horizon.
Midnight. Two faint beams to the N[orth]. E[ast]. & strongly define lance shaped, a
parallel ones to S[outh]. W[est].
Should you think this account of any value, perhaps you
[[8]] will kindly communicate it to the Philosophical Club & the Athenaeum or make
whatever use of it you deem proper. I shall not fail to collect any notices of the
Phenomena that may occur in India.
ENDNOTES
1. This letter is a copy written in a hand not that of the original author, JDH, and is
unsigned. The copy was probably written or by JDH's mother or sister.
2. The current name of the city of Calcutta is Kolkata
3. The current name of the city of Madras is Chennai.
4. The mountain which JDH refers to as "Paris--Nath" or "Paras--Nath" is now
more commonly known as Parasnath or Shikharji.
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