_VOYAGE TO ALGERIA TO OBSERVE THE ECLIPSE._
The opening of the Eclipse Expedition was not propitious. Portsmouth,
on the 5th of December 1870, was swathed by a fog, which was
intensified by smoke, and traversed by a drizzle of fine rain. At
six P.M. I was on board the ‘Urgent.’ On Tuesday morning the weather
was too thick to permit of the ship’s being swung and her compasses
calibrated. The Admiral of the port, a man of very noble presence, came
on board. Under his stimulus the energy which the weather had damped
appeared to become more active, and soon after his departure we steamed
down to Spithead. Here the fog had so far lightened as to enable the
officers to swing the ship.
At three P.M. on Tuesday the 6th of December we got away, gliding
successively past Whitecliff Bay, Bembridge, Sandown, Shanklin,
Ventnor, and St. Catherine’s Lighthouse. On Wednesday morning we
sighted the Isle of Ushant, on the French side of the Channel. The
northern end of the island has been fretted by the waves into detached
tower-like masses of rock of very remarkable appearance. In the
Channel the sea was green, and opposite Ushant it was a brighter green.
On Wednesday evening we committed ourselves to the Bay of Biscay.
The roll of the Atlantic was full, but not violent. There had been
scarcely a gleam of sunshine throughout the day, but the cloud-forms
were fine, and their apparent solidity impressive. On Thursday morning
I rose refreshed, and found the green of the sea displaced by a deep
indigo blue. The whole of Thursday we steamed across the bay. We had
little blue sky, but the clouds were again grand and varied--cirrus,
stratus, cumulus, and nimbus, we had them all. Dusky hairlike trails
were sometimes dropped from the distant clouds to the sea. These were
falling showers, and they sometimes occupied the whole horizon, while
we steamed across the rainless circle which was thus surrounded.
Sometimes we plunged into the rain, and once or twice, by slightly
changing course, avoided a heavy shower. From time to time perfect
rainbows spanned the heavens from side to side. At times a bow would
appear in fragments, showing the keystone of the arch midway in air,
and its two buttresses on the horizon. In all cases the light of the
bow could be quenched by a Nicol’s prism, with its long diagonal
tangent to the arc. Sometimes gleaming patches of the firmament were
seen amid the clouds. When viewed in the proper direction, the gleam
could be quenched by a Nicol prism, a dark aperture being thus opened
into stellar space.
At sunset on Thursday the denser clouds were fiercely fringed, while
through the lighter ones seemed to issue the glow of a conflagration.
On Friday morning we sighted Cape Finisterre, the extreme end of the
arc which sweeps from Ushant round the Bay of Biscay. Calm spaces of
blue, in which floated quietly scraps of cumuli, were behind us, but
in front of us was a horizon of portentous darkness. It continued thus
threatening throughout the day. Towards evening the wind strengthened
to a gale, and at dinner it was difficult to preserve the plates
and dishes from destruction. Our thinned company hinted that the
rolling had other consequences. It was very wild when we went to bed.
I slumbered and slept, but after some time was rendered actively
conscious that my body had become a kind of projectile, which had the
ship’s side for a target. I gripped the edge of my berth to save myself
from being thrown out. Outside, I could hear somebody say that he had
been thrown from his berth, and sent spinning to the other side of the
saloon. The screw laboured violently amid the lurching; it incessantly
quitted the water, and, twirling in the air, rattled against its
bearings, and caused the ship to shudder from stem to stern. At times
the waves struck us, not with the soft impact which might be expected
from a liquid, but with the sudden solid shock of battering-rams. ‘No
man knows the force of water,’ said one of the officers, ‘until he has
experienced a storm at sea.’ These blows followed each other at quicker
intervals, the screw rattling after each of them, until, finally,
the delivery of a heavier stroke than ordinary seemed to reduce the
saloon to chaos. Furniture crashed, glasses rang, and alarmed enquiries
immediately followed. Amid the noises I heard one note of forced
laughter; it sounded very ghastly. Men tramped through the saloon, and
busy voices were heard aft, as if something there had gone wrong.
I rose, and not without difficulty got into my clothes. In the
after-cabin, under the superintendence of the able and energetic
navigating lieutenant, Mr. Brown, a group of blue-jackets were working
at the tiller-ropes. These had become loose, and the helm refused to
answer the wheel. High moral lessons might be gained on shipboard by
observing what steadfast adherence to an object can accomplish, and
what large effects are heaped up by the addition of infinitesimals. The
tiller-rope, as the blue-jackets strained in concert, seemed hardly to
move; still it did move a little, until finally, by timing the pull to
the lurching of the ship, the mastery of the rudder was obtained. I had
previously gone on deck. Round the saloon-door were a few members of
the eclipse party, who seemed in no mood for scientific observation.
Nor did I; but I wished to see the storm. I climbed the steps to the
poop, exchanged a word with Captain Toynbee, the only member of the
party to be seen on the poop, and by his direction made towards a
cleat not far from the wheel.[44] Round it I coiled my arms. With the
exception of the men at the wheel, who stood as silent as corpses, I
was alone.
[44] The cleat is a T-shaped mass of metal employed for the fastening
of ropes.
I had seen grandeur elsewhere, but this was a new form of grandeur to
me. The ‘Urgent’ is long and narrow, and during our expedition she
lacked the steadying influence of sufficient ballast. She was for
a time practically rudderless, and lay in the trough of the sea. I
could see the long ridges, with some hundreds of feet between their
crests, rolling upon the ship perfectly parallel to her sides. As
they approached they so grew upon the eye as to render the expression
‘mountains high’ intelligible. At all events, there was no mistaking
their mechanical might, as they took the ship upon their shoulders, and
swung her like a pendulum. The poop sloped sometimes at an angle which
I estimated at over forty-five degrees; wanting my previous Alpine
practice, I should have felt less confidence in my grip of the cleat.
Here and there the long rollers were tossed by interference into heaps
of greater height. The wind caught their crests, and scattered them
over the sea, the whole surface of which was seething white. The aspect
of the clouds was a fit accompaniment to the fury of the ocean. The
moon was almost full--at times concealed, at times revealed, as the
scud flew wildly over it. These things appealed to the eye, while the
ear was filled by the whistle and boom of the storm and the groaning of
the screw.
Nor was the outward agitation the only object of interest to me. I
was at once subject and object to myself, and watched with intense
interest the workings of my own mind. The ‘Urgent’ is an elderly ship.
She had been built, I was told, by a contracting firm for some foreign
Government, and had been diverted from her first purpose when converted
into a troop-ship. She had been for some time out of work, and I had
heard that one of her boilers, at least, needed repair. Our scanty but
excellent crew, moreover, did not belong to the ‘Urgent,’ but had been
gathered from other ships. Our three lieutenants were also volunteers.
All this passed swiftly through my mind as the ship shook under the
blows of the waves, and I thought that probably no one on board could
say how much of this thumping and straining the ‘Urgent’ would be able
to bear. This uncertainty caused me to look steadily at the worst, and
I tried to strengthen myself in the face of it.
But at length the helm laid hold of the water, and the ship was got
gradually round to face the waves. The rolling diminished, a certain
amount of pitching taking its place. Our speed had fallen from eleven
knots to two. I went again to bed. After a space of calm, when we
seemed crossing the vortex of a storm, heavy tossing recommenced. I
was afraid to allow myself to fall asleep, as my berth was high, and
to be pitched out of it might be attended with bruises, if not with
fractures. From Friday at noon to Saturday at noon we accomplished
sixty-six miles, or an average of less than three miles an hour. I
overheard the sailors talking about this storm. The ‘Urgent,’ according
to those that knew her, had never previously experienced anything like
it.[45]
[45] There is, it will be seen, a fair agreement between these
impressions and those so vigorously described by a scientific
correspondent of the ‘Times.’
All through Saturday the wind, though somewhat sobered, blew dead
against us. The atmospheric effects were exceedingly fine. The
cumuli resembled mountains in shape, and their peaked summits shone
as white as Alpine snows. At one place this resemblance was greatly
strengthened by a vast area of cloud, uniformly illuminated, and lying
like a _névé_ below the peaks. From it fell a kind of cloud-river,
strikingly like a glacier. The horizon at sunset was remarkable--spaces
of brilliant green between clouds of fiery red. Rainbows had been
frequent throughout the day, and at night a perfectly continuous lunar
bow spanned the heavens from side to side. Its colours were feeble;
but, contrasted with the black ground against which it rested, its
luminousness was extraordinary.
Sunday morning found us opposite to Lisbon, and at midnight we rounded
Cape St. Vincent, where the lurching seemed disposed to recommence.
Through the kindness of Lieutenant Walton, a cot had been slung for me.
It hung between a tiller-wheel and a flue, and at one A.M. I was roused
by the banging of the cot against its boundaries. But the wind was
now behind us, and we went along at a speed of eleven knots. We felt
certain of reaching Cadiz by three. But a new lighthouse came in sight,
which some affirmed to be Cadiz lighthouse, while the surrounding
houses were declared to be Cadiz itself. Out of deference to these
statements, the navigating lieutenant changed his course, and steered
for the place. A pilot came on board, and he informed us that we were
before the mouth of the Guadalquivir, and that the lighthouse was that
of Cipiòna. Cadiz was still some eighteen miles distant.
We steered towards the city, hoping to get into the harbour before
dark. But the pilot was snapped up by another vessel, and we did not
get in. We beat about during the night, and in the morning found
ourselves about fifteen miles from Cadiz. The sun rose behind the city,
and we steered straight into the light. The three-towered cathedral
stood in the midst, round which swarmed apparently a multitude of
chimney-stacks. A nearer approach showed the chimneys to be small
turrets. A pilot was taken on board; for there is a dangerous shoal
in the harbour. The appearance of the town as the sun shone upon its
white and lofty walls was singularly beautiful. We cast anchor; some
officials arrived and demanded a clean bill of health. We had none.
They would have nothing to do with us; so the yellow quarantine flag
was hoisted, and we waited for permission to land the Cadiz party.
After some hours of delay the English consul and vice-consul came
on board, and with them a Spanish officer, ablaze with gold lace
and decorations. Under slight pressure the requisite permission had
been granted. We landed our party, and in the afternoon weighed
anchor. Thanks to the kindness of our excellent paymaster, I was here
transferred to a roomier berth.
Cadiz soon sank beneath the sea, and we sighted in succession Cape
Trafalgar, Tarifa, and the revolving light of Ceuta. The water was
very calm, and the moon rose in a quiet heaven. She swung with her
convex surface downwards, the common boundary between light and
shadow being almost horizontal. A pillar of reflected light shimmered
up to us from the slightly rippled sea. I had already noticed the
phosphorescence of the water, but to-night it was stronger than usual,
especially among the foam at the bows. A bucket let down into the sea
brought up a number of the little sparkling organisms which cause
the phosphorescence. I caught some of them in my hand. And here an
appearance was observed which was new to most of us, and strikingly
beautiful to all. Standing at the bow and looking forwards, at a
distance of forty or fifty yards from the ship a number of luminous
streamers were seen rushing towards us. On nearing the vessel they
rapidly turned, like a comet round its perihelion, placed themselves
side by side, and, as parallel trails of light, kept up with the ship.
One of them placed itself right in front of the bow as a pioneer.
These comets of the sea were joined at intervals by others. Sometimes
as many as six at a time would rush at us, bend with extraordinary
rapidity round a sharp curve, and afterwards keep us company. Leaning
over the bow, and scanning the streamers closely, the frontal portion
of each revealed the outline of a porpoise. The rush of the creatures
through the water had started the phosphorescence, every spark of which
was converted by the motion of the retina into a line of light. Each
porpoise was thus wrapped in a luminous sheath. The phosphorescence did
not cease at the creature’s tail, but was carried many porpoise-lengths
behind it.
To our right we had the African hills, illuminated by the moon.
Gibraltar Rock at length became visible, but the town remained long
hidden by a belt of haze. Through this at length the brighter lamps
struggled. It was like the gradual resolution of a nebula into stars.
As the intervening depth became gradually less the mist vanished more
and more, and finally all the lamps shone through it. They formed a
bright foil to the sombre mass of rock above them. The sea was so calm
and the scene so lovely that Mr. Huggins and myself stayed on deck till
the ship was moored, near midnight. During our walking to and fro a
striking enlargement of the disc of Jupiter was observed whenever the
heated air of the funnels came between us and the planet. On passing
away from the heated air, the flat dim disc would immediately shrink
to a luminous point. The effect was one of retinal persistence. The
retinal image of the planet was set quivering in all azimuths by the
streams of heated air, describing in quick succession minute lines of
light, which summed themselves to a disc of sensible area.
At six o’clock next morning the gun at the signal station on the
summit of the rock boomed. At eight the band on board the ‘Trafalgar’
training-ship, which was in the harbour, struck up the national anthem;
and immediately afterwards a crowd of mite-like cadets swarmed up the
rigging. After the removal of the apparatus belonging to the Gibraltar
party we went on shore. Winter was in England when we left, but here
we had the warmth of summer. The vegetation was luxuriant--palm-trees,
cactuses, and aloes, all ablaze with scarlet flowers. A visit to
the Governor was proposed, as an act of necessary courtesy, and
I accompanied Admiral Ommaney and Mr. Huggins to the Convent, or
Government House. We sent in our cards, waited for a time, and were
then conducted by an orderly to his Excellency. He is a fine old man,
over six foot high, and of frank military bearing. He received us
and conversed with us in a very genial manner. He took us to see his
garden, his palms, his shaded promenades, and his orange-trees loaded
with fruit, in all of which he took manifest delight. Evidently ‘the
hero of Kars’ had fallen upon quarters after his own heart. He appeared
full of good nature, and engaged us on the spot to dine with him that
day.
We sought the town-major for a pass to visit the lines. While awaiting
his arrival I purchased a stock of white glass bottles, with a view
to experiments on the colour of the sea. Mr. Huggins and myself,
who wished to see the rock, were taken by Captain Salmond to the
library, where a model of Gibraltar is kept, and where we had a capital
preliminary lesson. At the library we met Colonel Maberly, a courteous
and kindly man, who gave us good advice regarding our excursion. He
sent an orderly with us to the entrance of the lines. The orderly
handed us over to an intelligent Irishman, who was directed to show
us everything that we desired to see, and to hide nothing from us.
We took the ‘upper lines,’ traversed the galleries hewn through the
limestone, looked through the embrasures, which opened like doors in
the precipice, over the hills of Spain, reached St. George’s Hall, and
went still higher, emerging on the summit of one of the noblest cliffs
I have ever seen.
Beyond were the Spanish lines, marked by a line of white sentry-boxes;
nearer were the English lines, less conspicuously marked out; and
between both was the neutral ground. Behind the Spanish lines was the
conical hill called the Queen of Spain’s Chair. The general aspect
of Spain from the rock is bold and rugged. Doubling back from the
galleries, we struck upwards towards the crest, reached the signal
station, where we indulged in shandy-gaff and bread and cheese. Thence
to O’Hara’s Tower, the highest point of the rock. It was built by a
former Governor, who, forgetful of the laws of terrestrial curvature,
thought he might look from the tower into the port of Cadiz. The tower
is riven, and may be climbed along the edges of the crack. We got to
the top of it; thence descended the curious Mediterranean Stair--a
zigzag, mostly of steps down a steeply falling slope, amid palmetto
brush, aloes, and prickly pear.
Passing over the Windmill Hill, we were joined at the ‘Governor’s
Cottage’ by a car, and drove afterwards to the lighthouse at Europa
Point. The tower was built, I believe, by Queen Adelaide, and it
contains a fine dioptric apparatus of the first order, constructed by
the Messrs. Chance of Birmingham. At the appointed hour we were at the
Convent. During dinner the same genial traits which appeared in the
morning were still more conspicuous. The freshness of the Governor’s
nature showed itself best when he spoke of his old antagonist in arms,
Mouravieff. Chivalry in war is consistent with its stern prosecution.
These two men were chivalrous, and after striking the last blow became
friends for ever. Our kind and courteous reception at Gibraltar is a
thing to be remembered with pleasure.
On the 15th of December we committed our selves to the Mediterranean.
The views of Gibraltar with which we are most acquainted represent it
as a huge ridge; but its aspect, end on, both from the Spanish lines
and from the other side, is truly noble. There is a sloping bank of
sand at the back of the rock, which I was disposed to regard simply as
the _débris_ of the limestone. I wished to let myself down upon it, but
had not the time. My friend Mr. Busk, however, assures me that it is
silica, and that the same sand constitutes the adjacent neutral ground.
There are theories afloat as to its having been blown from Sahara.
The Mediterranean throughout this first day, and indeed throughout
the entire voyage to Oran, was of less deep a blue than the Atlantic.
Possibly the quantity of organisms may have modified the colour. At
night the phosphorescence was delicious, breaking with the suddenness
of a snapped spring along the crests of the waves formed by the port
and starboard bows. Its strength was not uniform. Having flashed
brilliantly for a time, it would in part subside, and afterwards regain
its vigour. Several large phosphorescent masses of weird appearance
also floated past.
On the morning of the 16th we sighted the fort and lighthouse of Marsa
el Kibir, and beyond them the white walls of Oran lying in the bight
of a bay, sheltered by dominant hills. The sun was shining brightly;
during our whole voyage we had not had so fine a day. The wisdom
which had led us to choose Oran as our place of observation seemed
demonstrated. A rather excitable pilot came on board, and he guided us
in behind the Mole, which had suffered much damage last year from an
unexplained outburst of waves from the Mediterranean. Both port and bow
anchors were cast into deep water. With three huge hawsers the ship’s
stern was made fast to three gun-pillars fixed in the Mole; and here
for a time the ‘Urgent’ rested from her labours.
M. Janssen, who had rendered his name celebrated by his observations
of the eclipse in India in 1868, when he showed the solar flames to
be eruptions of incandescent hydrogen, was already encamped in the
open country about eight miles from Oran. On the 2nd of December he
had quitted Paris in a balloon, with a strong young sailor as his
assistant, had descended near the mouth of the Loire, seen M. Gambetta,
and received from him encouragement and aid. On the day of our arrival
his encampment was visited by Mr. Huggins, and the kind and courteous
Engineer of the Port drove me subsequently in his own phaeton to the
place. It bore the best repute as regards freedom from haze and fog,
and commanded an open outlook, but it was inconvenient for us on
account of its distance from the ship. The place next in repute was the
railway station, between two and three miles distant from the Mole. It
was inspected, but, being enclosed, was abandoned for an eminence in
an adjacent garden, the property of Mr. Hinshelwood, a Scotchman who
had settled some years previously as an esparto merchant in Oran,[46]
and who in the most liberal manner placed his ground at the disposition
of the party. Here the tents were pitched on the Saturday by Captain
Salmond and his intelligent corps of sappers, the instruments being
erected on the Monday under cover of the tents.
[46] Esparto is a kind of grass now much used in the manufacture of
paper.
Close to the railway station runs a new loopholed wall of defence,
through which the highway passes into the open country. Standing on the
highway, and looking southwards, about twenty yards to the right is a
small bastionet, intended to carry a gun or two. Its roof I thought
would form an admirable basis for my telescope, while the view of the
surrounding country was unimpeded in all directions. The authorities
kindly allowed me the use of this bastionet. Two men, one a blue-jacket
named Elliot, and the other a marine named Hill, were placed at my
disposal by Lieutenant Walton; and thus aided, on Monday morning I
mounted my telescope. The instrument was new to me, and I wished to
master all the details of its manipulation.
After some hours of discipline, and as the day was sobering towards
twilight, the telescope was dismounted and put under cover. Mr.
Huggins joined me, and we visited together the Arab quarter of Oran.
The flat-roofed houses appeared very clean and white. The street was
filled with loiterers, and the thresholds were occupied by picturesque
groups. Some of the men are very fine; we saw many straight, manly
fellows who must have been six foot four in height. They passed us
with perfect indifference, evincing no anger, suspicion, or curiosity,
hardly caring in fact to glance at us as we passed. In one instance
only during my stay at Oran was I spoken to by an Arab. He was a tall,
good-humoured fellow, who came smiling up to me, and muttered something
about ‘les Anglais.’ The mixed population of Oran is picturesque in
the highest degree: the Jews, rich and poor, varying in their costumes
as their wealth varies--the Arabs more picturesque still, and of all
shades of complexion--the negroes, the Spaniards, the French, all
grouped together, and each preserving their own individuality, formed a
picture intensely interesting me.
On Tuesday, the 20th, I was early at the bastionet, with the view of
schooling both myself and my men. The night had been very squally. The
sergeant of the sappers took charge of our key, and on Tuesday morning
Elliot went for it. He brought back the intelligence that the tents
had been blown down, and the instruments overturned. Among these was a
large and valuable equatorial from the Royal Observatory, Greenwich.
It seemed hardly possible that this instrument, with its wheels and
verniers and delicate adjustments, could have escaped uninjured from
such a fall. This, however, was the case; and during the day all the
overturned instruments were restored to their places, and found to be
in practical working order. This and the following day were devoted
to incessant schooling. I had come out as a general star-gazer, and
not with the intention of devoting myself to the observation of any
particular phenomenon. I wished to see the whole--the first contact,
the advance of the moon, and the successive swallowing up of the solar
spots, the breaking of the last line of crescent by the lunar mountains
into Bailey’s beads, the advance of the shadow through the air, the
appearance of the corona and prominences at the moment of totality, the
radiant streamers of the corona, the internal structure of the flames,
a glance through a polariscope, a sweep round the landscape with the
naked eye, the reappearance of the solar limb through Bailey’s beads,
and, finally, the retreat of the lunar shadow through the air.
For these observations I was provided with a telescope of admirable
definition, mounted, adjusted, packed, and most liberally placed at my
disposal by Mr. Warren De la Rue. The telescope grasped the whole of
the sun, and a considerable portion of the space surrounding it. But it
would not take in the probable extreme limits of the corona. For this
the ‘finder’ was suitable; but, instead of it, I had lashed on to the
large telescope a light but powerful instrument, constructed by Ross,
and lent to me by Mr. Huggins. I was also furnished with an excellent
binocular by Mr. Dallmeyer. In fact, no man could have been more
efficiently supported than I was. It required a strict parcelling out
of the two minutes and some seconds of totality to embrace in them the
entire series of observations. These, while the sun remained visible,
were to be made with an unsilvered diagonal eyepiece, which reflected
but a small fraction of the sun’s light, this fraction being still
further toned down by a dark glass. At the moment of totality the dark
glass was to be removed, and a silver reflector pushed in, so as to
get the maximum of light from the corona and prominences. The time of
totality was distributed as follows:
1. Observe approach of shadow through the air: totality.
2. Telescope 30 seconds.
3. Finder 30 seconds.
4. Double image prism 15 seconds.
5. Naked eye 10 seconds.
6. Finder or binocular 20 seconds.
7. Telescope 20 seconds.
8. Observe retreat of shadow.
It was proposed to begin and end with the telescope, so that any change
in the field of view occurring during the totality might be noticed.
Elliot stood beside me, watch in hand, and furnished with a lantern.
He called out at the end of each interval, and I moved from telescope
to finder, from finder to polariscope, from polariscope to naked eye,
from naked eye back to finder, from finder to telescope, abandoning the
instrument finally to observe the retreating shadow. All this we went
over twenty times, while looking at the actual sun, and keeping him in
the middle of the field. It was my object to render the repetition of
the lesson so mechanical as to leave no room for flurry, forgetfulness,
or excitement. Volition was not to be called upon, nor judgment
exercised, but a well-beaten path of routine was to be followed.
Had the opportunity occurred, I think the programme would have been
strictly carried out.
But the opportunity did not occur. For several days the weather had
been ill-natured. We had wind so strong as to render the hawsers at
the stern of the ‘Urgent’ as rigid as iron, and, therefore, to destroy
the navigating lieutenant’s sleep. We had clouds, a thunder-storm,
and some rain. Still the hope was held out that the atmosphere would
cleanse itself, and if it did we were promised an air of extraordinary
limpidity. Early on the 22nd we were all at our posts. Spaces of blue
in the early morning gave us some encouragement, but all depended on
the relation of these spaces to the surrounding clouds. Which of them
were to grow as the day advanced? The wind was high, and to secure the
steadiness of my instrument I was forced to retreat behind a projection
of the bastionet, place stones upon its stand, and, further, to avail
myself of the shelter of a sail. My practised men fastened the sail
at the top, and loaded it with boulders at the bottom. It was tried
severely, but it stood firm.
The clouds and blue spaces fought for a time with varying success.
The sun was hidden and revealed at intervals, hope oscillating in
synchronism with the changes of the sky. At the moment of first contact
a dense cloud intervened, but a minute or two afterwards the cloud had
passed, and the encroachment of the black body of the moon was evident
upon the solar disc. The moon marched onward, and I saw it at frequent
intervals; a large group of spots were approached and swallowed up.
Subsequently I caught sight of the lunar limb as it cut through the
middle of a large spot. The spot was not to be distinguished from the
moon, but rose like a mountain above it. The clouds, when thin, could
be seen as grey scud drifting across the black surface of the moon;
but they thickened more and more, and made the intervals of clearness
scantier. During these moments I watched with an interest bordering
upon fascination the march of the silver sickle of the sun across the
field of the telescope. It was so sharp and so beautiful. No trace
of the lunar limb could be observed beyond the sun’s boundary. Here,
indeed, it could only be relieved by the corona, which was utterly cut
off by the dark glass. The blackness of the moon beyond the sun was, in
fact, confounded with the blackness of space.
Beside me was Elliot with the watch and lantern, while Lieutenant
Archer, of the Royal Engineers, had the kindness to take charge of
my note-book. I mentioned, and he wrote rapidly down, such things as
seemed worthy of remembrance. Thus my hands and mind were entirely
free; but it was all to no purpose. A patch of sunlight fell and rested
upon the landscape some miles away. It was the only illuminated spot
within view. But to the north-west there was still a space of blue
which might reach us in time. Within seven minutes of totality another
small space towards the zenith became very dark. The atmosphere was,
as it were, on the brink of a precipice; it was charged with humidity,
which required but a slight chill to bring it down in clouds. This was
furnished by the withdrawal of the solar beams; the clouds did come
down, covering up the space of blue on which our hopes had so long
rested. I abandoned the telescope and walked to and fro, like a leopard
in its cage. As the moment of totality approached, the descent towards
darkness was as obvious as a falling stone. I looked towards a distant
ridge, where I knew the darkness would first appear. At the moment a
fan of beams, issuing from the hidden sun, was spread out over the
southern heavens. These beams are bars of alternate light and shade,
produced in illuminated haze by the shadows of floating cloudlets of
varying density. The beams are really parallel, but by an effect of
perspective they appear divergent, like a fan, having the sun, in fact,
for their point of intersection. The darkness took possession of the
ridge to which I have referred, lowered upon M. Janssen’s observatory,
passed over the southern heavens, blotting out the beams as if a
sponge had been drawn across them. It then took successive possession
of three spaces of blue sky in the south-eastern atmosphere. I again
looked towards the ridge. A glimmer as of day-dawn was behind it, and
immediately afterwards the fan of beams which had been for more than
two minutes absent revived. The eclipse of 1870 had ended, and, as far
as the corona was concerned, we had been defeated.
Even in the heart of the eclipse the darkness was by no means perfect.
Small print could be read. In fact, the clouds which rendered the
day a dark one, by scattering light into the shadow, rendered it
less intense than it would have been had the atmosphere been without
cloud. In the more open spaces I sought for stars, but could find
none. There was a lull in the wind before and after totality, but
during the totality the wind was strong. I waited for some time on the
bastionet, hoping to get a glimpse of the moon on the opposite border
of the sun, but in vain. The clouds continued, and some rain fell.
The day brightened somewhat afterwards, and, having packed all up, in
the sober twilight Mr. Crookes and myself climbed the heights above
the fort of Vera Cruz. From this eminence we had a very noble view
over the Mediterranean and the flanking African hills. The sunset was
remarkable, and the whole outlook exceedingly fine.
The able and well-instructed medical officer of the ‘Urgent,’ Mr.
Goodman, observed the following temperatures during the progress of the
eclipse:
Hour Deg.
11.45 56
11.55 55
12.10 54
12.37 53
12.39 52
12.43 51
1.5 52
1.27 53
1.44 56
2.10 57
The minimum temperature occurred some minutes after totality, when a
slight rain fell.
The wind was so strong on the 23rd that Captain Henderson would not
venture out. Guided by Mr. Goodman, I visited a cave scooped into a
remarkable stratum of shell-breccia, and, thanks to my guide, secured
specimens. Mr. Busk informs me that a precisely similar breccia
is found at Gibraltar at approximately the same level. During the
afternoon Admiral Ommaney and myself drove to the fort of Marsa el
Kibir. The fortification is of ancient origin, the Moorish arches being
still there in decay, but the fort is now very strong. About four or
five hundred dragoons, fine-looking men, were looking after their
horses, waiting for a lull to enable them to embark for France. One of
their officers was wandering in a very solitary fashion over the fort.
We had some conversation with him. He had been at Sedan, had been taken
prisoner, but had effected his escape. He shook his head when we spoke
of the termination of the war, and predicted its long continuance.
There was bitterness in his tone as he spoke of the charges of treason
which had been so lightly levelled against French commanders. The green
waves raved round the promontory on which the fort stands, smiting the
rocks, breaking into snow, and jumping, after impact, to a height of
a hundred feet and more into the air. On our return our vehicle broke
down through the loss of a wheel. The Admiral went on board, while I
hung long over the agitated sea. The little horses of Oran well merit a
passing word. Their speed and endurance, which are both heavily drawn
upon by their drivers, are extraordinary.
The wind sinking, we lifted anchor on the 24th. For some hours we went
pleasantly along; but during the afternoon the storm revived, and it
blew heavily against us all the night. When we came opposite the Bay
of Almeria, on the 25th, the captain turned the ship, and steered
into the bay, where, under the shadow of the Sierra Nevada, we passed
Christmas night in peace. Next morning ‘a rose of dawn’ rested on the
snows of the adjacent mountains, while a purple haze was spread over
the lower hills. I had no notion that Spain possessed so fine a range
of mountains as the Sierra Nevada. The height is considerable, but the
form also is such as to get the maximum of grandeur out of the height.
We got away at eight A.M., passing for a time through shoal water, the
bottom of which had been evidently stirred up. The adjacent land seemed
eroded in a remarkable manner. Doubtless it has its times of flood,
which excavate these valleys and ravines, and leave those singular
ridges behind. Towards evening I climbed the mainmast, and, standing
on the crosstrees, saw the sun set amid a blaze of fiery clouds. The
wind was strong and bitterly cold, and I was glad to return to the deck
along a rope which stretched from the mast-head to the ship’s side.
That night we cast anchor beside the Mole of Gibraltar.
On the morning of the 27th, in company with two friends, I drove to
the Spanish lines, with the view of seeing the rock from that side. It
is an exceedingly noble mass. The Peninsular and Oriental mail-boat
had been signalled and had come. Heavy duties called me homeward, and
by transferring myself from the ‘Urgent’ to the mail-steamer I should
gain three days. I hired a boat, rowed to the steamer, learned that
she was to start at one, and returned with all speed to the ‘Urgent.’
Making known to Captain Henderson my wish to get away, he expressed
doubts as to the possibility of reaching the mail-steamer in time. With
his accustomed kindness, he, however, placed a boat at my disposal.
Four hardy fellows and one of the ship’s officers jumped into it; my
luggage, hastily thrown together, was tumbled in afterwards, and we
were immediately on our way. We had nearly four miles to row in about
twenty minutes; but we hoped the mail-boat might not be punctual. For a
time we watched her anxiously; there was no motion; we came nearer, but
the flags were not yet hauled in. The men put forth all their strength,
animated by the exhortations of the officer at the helm. The roughness
of the sea rendered their efforts to some extent nugatory: still we
were rapidly approaching the steamer. At length she moved, punctually
almost to the minute, at first slowly, but soon with quickened pace. We
turned to the left, so as to cut across her bows. Five minutes’ pull
would have brought us up to her. The officer waved his cap and I my
hat. ‘If they could only see us, they might back to us in a moment.’
But they did not see us, or if they did, they paid no attention to
us. I returned to the ‘Urgent,’ discomfited, but grateful to the fine
fellows who had wrought so hard to carry out my wishes.
Glad of the quiet, in the sober afternoon I took a walk towards Europa
Point. The sky darkened, and heavy squalls passed at intervals. Rain
began to fall, and I returned home. Private theatricals were at the
Convent, and the kind and courteous Governor had sent cards to the
eclipse party. I failed in my duty in not going. I had heard of St.
Michael’s Cave as rivalling, if not outrivalling, the Mammoth Cave of
Kentucky. On the 28th Messrs. Crookes, Carpenter, and myself, guided
by a military policeman who understood his work, explored the cavern.
The mouth is about 1,100 feet above the sea. We zigzagged up to it,
and first were led into an aperture in the rock some height above the
true entrance of the cave. In this upper cavern we saw some tall and
beautiful stalactite pillars.
The water drips from the roof charged with bicarbonate of lime.
Exposed to the air, the carbonic acid partially escapes, and the
simple carbonate of lime, which is hardly at all soluble in water,
deposits itself as a solid, forming stalactites and stalagmites. Even
the exposure of chalk or limestone water to the open air partially
softens it. A specimen of the Redbourne water exposed by Messrs.
Graham, Miller, and Hofmann in a shallow basin, fell from eighteen
degrees to nine degrees of hardness. The softening process of Clark is
virtually a hastening of the natural process. Here, however, instead of
being permitted to evaporate, half the carbonic acid is appropriated
by lime, the half thus taken up, as well as the remaining half, being
precipitated. The solid precipitate is permitted to sink, and the clear
supernatant liquid is limpid soft water.
We returned to the real mouth of St. Michael’s Cave, which is entered
by a wicket. The floor was somewhat muddy, and the roof and walls were
wet. Our guide took off his coat, but we did not follow his example. We
were soon in the midst of a natural temple, where tall columns sprang
complete from floor to roof, while incipient columns were growing
to meet each other, upwards and downwards. The water which trickles
from the stalactite, after having in part yielded up its carbonate of
lime, falls upon the floor vertically underneath, and there builds
the stalagmite. Consequently, the pillars grow from above and below
simultaneously along the same vertical. It is easy to distinguish the
stalagmitic from the stalactitic portion of the pillars. The former
is always divided into short segments by protuberant rings, as if
deposited periodically, while the latter presents a uniform surface.
In some cases the points of inverted cones of stalactite rested on the
centres of pillars of stalagmite. The process of solidification and the
architecture were alike beautiful.
We followed our guide through various branches and arms of the cave,
climbed and descended steps, halted at the edges of dark shafts and
apertures, squeezed ourselves through narrow passages, where the sober
grey of my coat suffered less than the black of my companions’. From
time to time we halted, while Mr. Crookes illuminated with ignited
magnesium wire the roof, columns, dependent spears, and graceful
drapery of the stalactite. Once, coming to a magnificent cluster of
icicle-like spears, we helped ourselves to specimens. There was some
difficulty in detaching the more delicate ones, their fragility was so
great. A consciousness of vandalism which smote me at the time haunts
me still; for, though our requisitions were moderate, this beauty ought
not to be at all invaded. Pendent from the roof in their natural
habitat, nothing can exceed their delicate beauty; they _live_, as it
were, surrounded by organic connections. In London they are curious,
but not beautiful. Of gathered shells Emerson writes:
I wiped away the weeds and foam,
And brought my sea-born treasures home:
But the poor, unsightly, noisome things
Had left their beauty on the shore,
With the sun, and the sand, and the wild uproar.
The promontory of Gibraltar is so burrowed with caverns that it has
been called the Hill of Caves. They are apparently related to the
geologic disturbances which the rock has undergone. The earliest
of these is the tilting of the once horizontal strata. Suppose a
force acting upon the promontory at its southern extremity, near
Europa Point, tending to twist the strata in a direction opposed
to that of the hands of a watch, and suppose the rock to be of a
partially yielding character, such a force would turn the strata into
screw-surfaces, the greatest amount of twisting being endured near the
point of application of the force. Such a twisting the rock appears to
have suffered; but instead of the twist fading gradually and uniformly
off in passing from south to north, the want of uniformity in the
material has produced lines of dislocation where there are abrupt
changes in the amount of twist. Thus, at the northern end of the rock
the dip to the west is nineteen degrees; in the middle hill it is
thirty-eight degrees; in the centre of the south hill, or Sugar Loaf,
it is fifty-seven degrees. At the southern extremity of the Sugar Loaf
the strata are vertical, while further to the south they actually turn
over and dip to the east.
The rock is thus divided into three sections, separated from each other
by surfaces of dislocation, where the rock is much wrenched and broken.
These places of dislocation are called the Northern and Southern
Quebrada, from the Spanish ‘Tierra Quebrada,’ or broken ground; and
it is at these places that the inland caves of Gibraltar are almost
exclusively found. Based on the observations of Dr. Falconer and
himself, an excellent and most interesting account of these caves, and
of the human remains and works of art which they contain, was given
by Mr. Busk at the meeting of the Congress of Prehistoric Archæology
at Norwich, and afterwards printed in the ‘Transactions’ of the
Congress.[47] Long subsequently to the operation of the twisting force
just referred to, the promontory underwent various changes of level.
There are sea-terraces and layers of shell-breccia along its flanks,
and numerous caves which, unlike the inland one, are the product of
marine erosion. The Apes’ Hill, on the African side of the strait, Mr.
Busk informs me has undergone similar disturbances.[48]
[47] In this essay Mr. Busk refers to the previous labours of Mr.
Smith, of Jordan Hill, to whom we owe most of our knowledge of the
geology of the rock.
[48] No one can rise from the perusal of Mr. Busk’s paper without a
feeling of admiration for the principal discoverer and indefatigable
explorer of the Gibraltar caves, the late Captain Frederick Brome.
In the harbour of Gibraltar, on the morning of our departure, I resumed
a series of observations on the colour of the sea. On my way out I had
collected a number of specimens, with a view to subsequent examination.
But the bottles were claret bottles, and I could by no means feel sure
of their purity. At Gibraltar, therefore, I purchased fifteen white
glass bottles, with ground glass stoppers, and at Cadiz, thanks to
the friendly guidance of Mr. Cameron, I secured a dozen more. These
seven-and-twenty bottles were filled with water, taken at different
places between Oran and Spithead.
And here let me express my warmest acknowledgments to Captain
Henderson, the commander of H.M.S. ‘Urgent,’ who aided me in my
observations in every possible way. Indeed, my best thanks are due to
all the officers for their unfailing courtesy and help. The captain
placed at my disposal his own coxswain, an intelligent fellow named
Thorogood, who skilfully attached a cord to each bottle, weighted it
with lead, cast it into the sea, and, after three successive rinsings,
filled it under my own eyes. The contact of jugs, buckets, or other
vessels was thus avoided, and even the necessity of pouring the water
out afterwards through the dirty London air.
The mode of examination applied to these bottles after my return to
London is in some sense complementary to that of the microscope, and
may I think materially aid enquiries conducted with that instrument. In
microscopic examination attention is directed to a small portion of the
liquid, the aim being to detect the individual suspended particles. In
my case, a large portion of the liquid is illuminated by a powerfully
condensed beam, its general condition being revealed through the light
scattered by suspended particles. Care is taken to defend the eye from
the access of all other light, and, thus defended, it becomes an organ
of inconceivable delicacy. Were water of uniform density perfectly free
from suspended matter, it would, in my opinion, scatter no light at
all. The track of a luminous beam could not, I think, be seen in such
water. But an amount of impurity so infinitesimal as to be scarcely
expressible in numbers, and the individual particles of which are so
small as wholly to elude the microscope, may, when examined by the
method alluded to, produce not only sensible, but striking, effects
upon the eye.
The results of the examination of nineteen bottles, filled at various
places between Gibraltar and Spithead, are here tabulated:
No.| Locality |Colour of Sea|Appearance in Electric Beam
---+-------------------------+-------------+------------------------------
1 |Gibraltar Harbour |Green |Thick with fine particles
2 |Two miles from Gibraltar |Clearer green|Thick with very fine particles
3 |Off Cabreta Point |Bright green |Still thick, but less so
4 |Off Cabreta Point |Black-indigo |Much less thick, very pure
5 |Off Tarifa |Undecided |Thicker than No. 4
6 |Beyond Tarifa |Cobalt-blue |Much purer than No. 5
7 |Twelve miles from Cadiz |Yellow-green |Very thick
8 |Cadiz Harbour |Yellow-green |Exceedingly thick
9 |Fourteen miles from Cadiz|Yellow-green |Thick, but less so
10 |Fourteen miles from Cadiz|Bright green |Much less thick
11 |Between Capes St. Mary | |
| and Vincent |Deep indigo | Very little matter, very pure
12 |Off the Burlings |Strong green |Thick with fine matter
13 |Beyond the Burlings |Indigo |Very little matter, pure
14 |Off Cape Finisterre |Undecided |Less pure
15 |Bay of Biscay |Black-indigo |Very little matter, very pure
16 |Bay of Biscay |Indigo |Very fine matter, Iridescent
17 |Off Ushant |Dark green |A good deal of matter
18 |Off St. Catherine’s |Yellow green |Exceedingly thick
19 |Spithead |Green |Exceedingly thick
Here, in the first instance, we have three specimens of water,
described as green, a clearer green, and bright green, taken in
Gibraltar Harbour, at a point two miles from the harbour, and off
Cabreta Point. The home examination showed that the first was thick
with suspended matter, the second less thick, and the third still less
thick. Thus the green brightened as the suspended matter became less.
Previous to the fourth observation our excellent navigating lieutenant,
Mr. Brown, steered along the coast, thus avoiding the adverse current
which sets in through the Strait of Gibraltar from the Atlantic to
the Mediterranean. He was at length forced to cross the boundary of
the Atlantic current, which was defined with extraordinary sharpness.
On the one side of it the water was a vivid green, on the other a deep
blue. Standing at the bow of the ship, a bottle could be filled with
blue water, while at the same moment a bottle cast from the stern could
be filled with bright green water. Two bottles were secured, one on
each side of this remarkable boundary. In the distance the Atlantic
had the hue called ultramarine; but looked fairly down upon, it was of
almost inky blackness--black qualified by a trace of indigo.
What change does the home examination here reveal? In passing to
indigo, the water becomes suddenly augmented in purity, the suspended
matter has become suddenly less. Off Tarifa, the deep indigo
disappears, and the sea is undecided in colour. Accompanying this
change, we have a rise in the quantity of suspended matter. Beyond
Tarifa, we change to cobalt-blue, the suspended matter falling at
the same time in quantity. This water is distinctly purer than the
green. We approach Cadiz, and at twelve miles from the city get into
yellow-green water; this the London examination shows to be thick with
suspended matter. The same is true of Cadiz Harbour, and also of a
point fourteen miles from Cadiz in the homeward direction. Here there
is a sudden change from yellow-green to a bright emerald-green, and
accompanying the change a sudden fall in the quantity of suspended
matter. Between Cape St. Mary and Cape St. Vincent the water changes to
the deepest indigo. In point of purity, this indigo water is shown by
the home examination to transcend the emerald-green water.
We now reach the remarkable group of rocks called the Burlings, and
find the water between the shore and the rocks a strong green; the
home examination shows it to be thick with fine matter. Fifteen or
twenty miles beyond the Burlings we come again into indigo water, from
which the suspended matter has in great part disappeared. Off Cape
Finisterre, about the place where the ‘Captain’ went down, the water
becomes green, and the home examination pronounces it to be thicker.
Then we enter the Bay of Biscay, where the indigo resumes its power,
and where the home examination shows the greatly augmented purity of
the water. A second specimen of water taken from the Bay of Biscay
held in suspension fine particles of a peculiar kind; the size of them
was such as to render the water richly iridescent. It showed itself
green, blue, or salmon colour, according to the direction of the line
of vision. Finally, we come to our last two bottles, the one taken
opposite St. Catherine’s lighthouse, in the Isle of Wight, the other at
Spithead. The sea at both these places was green, and both specimens,
as might be expected, were pronounced by the home examination to be
thick with suspended matter.
Two distinct series of observations are here referred to--the one
consisting of direct observations of the colour of the sea, conducted
during the voyage from Gibraltar to Portsmouth; the other conducted
in the laboratory of the Royal Institution. And here it is to be
noted that in the home examination I never knew what water I had in
my hands. The labels, which had written upon them the names of the
localities, had been tied up, all information regarding the source of
the water being thus precluded. The bottles were simply numbered, and
not till all the waters had been examined were the labels opened, and
the locality and sea-colour corresponding to the various specimens
ascertained. I must, therefore, have been perfectly unbiassed in my
home observations, and they, I think, clearly establish the association
of the green colour of sea-water with fine suspended matter, and the
association of the ultramarine colour, and more especially of the
black-indigo hue of sea-water, with the comparative absence of such
matter.
What, in the first place, is the cause of the dark hue of the deep
ocean?[49] A preliminary remark or two will clear our way towards an
explanation. Colour resides in white light, appearing generally when
any constituent of the white light is withdrawn. The hue of a purple
liquid, for example, is immediately accounted for by its action on a
spectrum. It cuts out the yellow and green, and allows the red and
blue to pass through. The blending of these two colours produces the
purple. But while the liquid attacks with special energy the yellow and
green colours, it enfeebles the whole spectrum; and by increasing the
thickness of the stratum we absorb the whole of the light. The colour
of a blue liquid is similarly accounted for. It first extinguishes the
red; then, as the thickness augments, it attacks the orange, yellow,
and green in succession; the blue alone finally remaining. But even it
might be extinguished by a sufficient depth of liquid.
[49] A note, written to me on October 22, by my friend Canon Kingsley,
contains the following reference to this point: ‘I have never seen the
Lake of Geneva, but I thought of the brilliant dazzling dark blue of
the mid-Atlantic under the sunlight, and its black-blue under cloud,
both so solid that one might leap off the sponson on to it without
fear; this was to me the most wonderful thing which I saw on my voyages
to and from the West Indies.’
And now we are prepared for a brief, but tolerably complete, statement
of the action of sea-water upon light, to which it owes its darkness.
The spectrum embraces three classes of rays--the thermal, the visual,
and the chemical. These divisions overlap each other; the thermal
rays are in part visual, the visual rays in part chemical, and
_vice versâ_. The vast body of thermal rays is beyond the red, being
invisible. These rays are attacked with exceeding energy by water.
They are absorbed close to the surface of the sea, and are the great
agents in evaporation. At the same time the whole spectrum suffers
enfeeblement; water attacks all its rays, but with different degrees
of energy. Of the visual rays, the red are attacked first, and first
extinguished. While the red is disappearing the remaining colours
are enfeebled. As the solar beam plunges deeper into the sea, orange
follows red, yellow follows orange, green follows yellow, and the
various shades of blue, where the water is deep enough, follow green.
Absolute extinction of the solar beam would be the consequence if the
water were deep and uniform; and if it contained no suspended matter,
such water would be as black as ink. A reflected glimmer of ordinary
light would reach us from its surface, as it would from the surface of
actual ink; but no light, hence no colour, would reach us from the body
of the water.
In very clear and very deep sea-water this condition is approximately
fulfilled, and hence the extraordinary darkness of such water. The
indigo, to which I have already referred, is, I believe, to be ascribed
in part to the suspended matter, which is never absent, even in the
purest natural water, and in part to the slight reflection of the
light from the limiting surfaces of strata of different densities.
A modicum of light is thus thrown back to the eye before the depth
necessary to absolute extinction has been attained. An effect precisely
similar occurs under the moraines of the Swiss glaciers. The ice here
is exceptionally compact, and, owing to the absence of the internal
scattering common in bubbled ice, the light plunges into the mass, is
extinguished, and the perfectly clear ice presents an appearance of
pitchy blackness.[50]
[50] I learn from a correspondent that certain Welsh tarns, which are
reputed bottomless, have this inky hue.
The green colour of the sea when it contains matter in a state of
mechanical suspension has now to be accounted for, and here, again,
let us fall back upon the sure basis of experiment. A strong white
dinner-plate was surrounded securely by cord, and had a lead weight
fastened to it. Fifty or sixty yards of strong hempen line were
attached to the plate. With it in his hand, my assistant, Thorogood,
occupied a boat fastened as usual to the davits of the ‘Urgent,’ while
I occupied a second boat nearer to the stern of the ship. He cast the
plate as a mariner heaves the lead, and by the time it had reached me
it had sunk a considerable depth in the water. In all cases the hue of
this plate was green: even when the sea was of the darkest indigo, the
green was vivid and pronounced. I could notice the gradual deepening of
the colour as the plate sank, but at its greatest depth in indigo water
the colour was still a blue-green.[51]
[51] In no case, of course, is the green pure, but a mixture of green
and blue.
Other observations confirmed this one. The ‘Urgent’ is a screw steamer,
and right over the blades of the screw was an orifice called the
screw-well, through which one could look from the poop down upon the
screw. The surface glimmer which so pesters the eye was here in a great
measure removed. Midway down a plank crossed the screw-well from side
to side, and on this I used to place myself to observe the action of
the screw underneath. The eye was rendered sensitive by the moderation
of the light, and, still further to remove all disturbing causes,
Lieutenant Walton had a sail and tarpaulin thrown over the mouth of
the well. Underneath this I perched myself and watched the screw. In
an indigo sea the play of colour was indescribably beautiful, and the
contrast between the water which had the screw-blades for a background,
and that which had the bottom of the ocean as a background, was
extraordinary. The one was of the most brilliant green, the other of
the deepest ultramarine. The surface of the water above the screw-blade
was always ruffled. Liquid lenses were thus formed, by which the
coloured light was withdrawn from some places and concentrated upon
others, the colour being thus caused to flash with metallic lustre. The
screw-blades in this case played the part of the plate in the former
case, and there were other instances of a similar kind. The white
bellies of the porpoises showed the green hue, varying in intensity
as the creatures swung to and fro between the surface and the deeper
water. Foam, at a certain depth below the surface, is also green. In a
rough sea the light which has penetrated the summit of a wave sometimes
reaches the eye, a beautiful green cap being thus placed upon the wave
even in indigo water.
But how is this colour to be connected philosophically with the
suspended particles? Take the dinner-plate which showed so brilliant
a green when thrown into indigo water. Suppose it to diminish in size
until it reaches an almost microscopic magnitude. It would still behave
substantially as the larger plate, sending to the eye its modicum of
green light. If the plate, instead of being a large coherent mass, were
ground to a powder sufficiently fine, and in this condition diffused
through the clear sea-water, it would send green light to the eye. In
fact, the suspended particles which the home examination reveals act in
all essential particulars like the plate, or like the screw-blades, or
like the foam, or like the bellies of the porpoises. Thus I think the
greenness of the sea is physically connected with the matter which it
holds in suspension.
We reached Portsmouth on the 5th of January 1871. There ended a voyage
which, though its main object was not realised, has left behind it
pleasant memories, both of the aspects of nature and the genial
kindliness of men.