Passages from the Life of a Philosopher/Chapter XVI
experience by fire.
Baked in an Oven—A Living Volcano—Vesuvius in action—Carried up the Cone of Ashes in a Chair—View of the Crater in a Dark Night—Sunrise—Descent by Ropes and Rolling into the great Crater—Watched the small Crater in active eruption at intervals—Measured a Base of 330 feet—Depth of great Crater 570 feet—Descent into small Crater—A Lake of red-hot Boiling Lava—Regained the great Crater with the sacrifice of my Boots—Lunched on Biscuits and Irish Whisky—Visit to the Hot Springs of Ischia—Towns destroyed by Earthquake—Coronets of Smoke projected by Vesuvius—Artificial Mode of producing them—Fire-damp visited in Welsh Coal-mine in company with Professor Moll.
Baked in an Oven.
Calling one morning upon Chantrey, I met Captain Kater and the late Sir Thomas Lawrence, the President of the Royal Academy. Chantrey was engaged at that period in casting a large bronze statue. An oven of considerable size had been built for the purpose of drying the moulds. I made several inquiries about it, and Chantrey kindly offered to let me pay it a visit, and thus ascertain by my own feelings the effects of high temperature on the human body.
I willingly accepted the proposal, and Captain Kater offered to accompany me. Sir Thomas Lawrence, who was suffering from indisposition, did not think it prudent to join our party. In fact, he died on the second or third day after our experiment
The iron folding-doors of the small room or oven were opened. Captain Kater and myself entered, and they were then closed upon us. The further corner of the room, which was paved with squared stones, was visibly of a dull-red heat. The thermometer marked, if I recollect rightly, 265°. The pulse was quickened, and I ought to have counted but did not count the number of inspirations per minute. Perspiration commenced immediately and was very copious. We remained, I believe, about five or six minutes without very great discomfort, and I experienced no subsequent inconvenience from the result of the experiment.
A Living Volcano.
I have never been so fortunate as to be conscious of having experienced the least shock of an earthquake, although, when a town had been destroyed in Ischia I hastened on from Rome in the hope of getting a slight shake. My passion was disappointed, so I consoled myself by a flirtation with a volcano.
The situation of my apartments during my residence at Naples enabled me constantly to see the cone of Vesuvius, and the continual projections of matter from its crater. Amongst these were occasionally certain globes of air, or of some gas, which, being shot upwards to a great height above the cone, spread out into huge coronets of smoke, having a singular motion amongst their particles.
A similar phenomenon sometimes occurs on a small scale during the firing of heavy ordnance. I have frequently seen such at Plymouth and elsewhere; but I was not satisfied about the cause of this phenomenon. I was told that it occurred more frequently if the muzzle of the gun were rubbed with grease; but this did not always succeed.
Soon after my return to London I made a kind of drum, by stretching wet parchment over a large tin funnel. On directing the point of the funnel at a candle placed a few feet distant, and giving a smart blow upon the parchment, it is observed that the candle is immediately extinguished.
This arises from what is called an air shot. In fact, the air in the tubular part is projected bodily forward, and so blows out the candle. The statements about persons being killed by cannon balls passing close to but not touching them, if true, are probably the results of air shots.
Wishing to trace the motions of such air shots, I added two small tubes towards the large end of the tin funnel, in order that I might fill it with smoke, and thus trace more distinctly the progress of the ball of air.
To my great delight the first blow produced a beautiful coronet of smoke, exactly resembling, on a small scale, the explosions from cannon or the still more attractive ones from Vesuvius.
If phosphoretted hydrogen or any other gas, which takes fire in air, were thus projected upwards, a very singular kind of fire-work would be produced.
It is possible in dark nights or in fogs that by such means signals might be made to communicate news or to warn vessels of danger.
Vesuvius was then in a state of moderate activity. It had a huge cone of ashes on its summit, surrounding an extensive crater of great depth. In one corner of this was a smaller crater, quite on a diminutive scale, which from time to time ejected red-hot fragments of lava occasionally to the height of from a thousand to fifteen hundred feet above the summit of the mountain.
I had taken apartments in the Chiaja, just opposite the volcano, in order that I might watch it with a telescope. In fact, as I lay in my bed I had an excellent view of the mountain. My next step was to consult with Salvatori, the most experienced of the guides, from whom I had purchased a good many minerals, as to the possibility of getting a peep down the volcano's throat.
Salvatori undertook to report to me from time to time the state of the mountain, round the base of which I made frequent excursions. After about a fortnight, the explosions were more regular and uniform, and Salvatori assured me that all the usual known indications led him to think that it was a fit time for my expedition. As I wished to see as much as possible, I made arrangements to economize my strength by using horses or mules to carry me wherever they could go. Where they could not carry me, as for instance, up the steep slope of the cone of ashes, I employed men to convey me in a chair.
By these means, I saw in the afternoon and evening of one day a good deal of the upper part of the mountain, then took a few hours' repose in a hut, and reached the summit of the cone long before sunrise.
It was still almost dark: we stood upon the irregular edge of a vast gulf spread out below at the depth of about five hundred feet. The plain at the bottom would have been invisible but for an irregular network of bright-red cracks spread over the whole of its surface. Now and then the silence was broken by a rush upwards of a flight of red-hot scoria from the diminutive crater within the large one. These missiles, however, although projected high above the summit of the cone, never extended themselves much beyond the small cavity from which they issued.
Those who have seen the blood-vessels of their own eye by the aid of artificial light, will have seen on a small scale a perfect resemblance of the plain which at that time formed the bottom of the great crater of Vesuvius.
As the morning advanced the light increased, and some time before sunrise we had completed the tour of the top of the great crater. Then followed that glorious sight—the sun when seen rising from the top of some lofty mountain.
I now began to speculate upon the means of getting a nearer view of the little miniature volcano in action at one corner of the gulf beneath us. We had brought ropes with us, and I had observed, in our tour round the crater, every dike of congealed lava by which the massive cone was split. These presented buttresses with frequent ledges or huge steps by which I hoped, with the aid of ropes, to descend into the Tartarus below.
Having consulted with our chief guide Salvatori, I found that he was unwilling to accompany us, and proposed remaining with the other guides on the upper edge of the crater. Upon the whole, I was not discontented with the arrangement, because it left a responsible person to keep the other guides in order, and also sufficient force to lift us up bodily by the ropes if that should become necessary.
The abruptness of the rocky buttresses compelled us to use ropes, but the attempt to traverse the steep inclines of light ashes and of fine sand would have been more dangerous from the risk of being engulfed in them.
Having well examined the several disadvantages of these rough-hewn irregular Titanic stairs, I selected one which seemed the most promising for facilitating our descent into the crater. I was encumbered with one of Troughton's heavy barometers, strapped to my back, looking much like Cupid's quiver, though probably rather heavier. In my pocket I had an excellent box sextant, and in a rough kind of basket two or three thermometers, a measuring tape, and a glass bottle enclosed in a leather case, commonly called a pocket-pistol, accompanied by a few biscuits.
We began our descent by the aid of two ropes, each supported above by two guides. I proceeded, trusting to my rope to step wherever I could, and then cautiously holding on by the rope to spring down to the next ledge. In this manner we descended until we arrived at the last projecting ledge of the dike. Nothing then remained for us but to slide down a steep and lengthened incline of fine sand. Fortunately, the sand itself was not very deep, and was supported by some solid material beneath it. I soon found that it was impossible to stand, so I sat down upon this moving mass, which evidently intended to accompany us in our journey. At first, to my great dismay, I was relieved from the care of my barometer, of which the runaway sand immediately took charge. I then found myself getting deeper and deeper in the sand, and still accelerating my downward velocity.
Gravity had at last done its work and became powerless. I soon dug myself out of my sandy couch, and rushed to my faithful barometer lying at some distance from me with its head just unburied. Fortunately, it was uninjured. My companion, with more skill or good fortune, or with less incumbrances, had safely alighted on the burning plain we now stood upon.
The area of this plain, for it was perfectly flat, was in shape somewhat elliptical. The surface consisted of a black scoriacious rock, reticulated with ditches from one to three feet wide, intersecting each other in every direction. From some of these, fumes not of the most agreeable odour were issuing. All those above two feet deep showed that at that depth below us everything was of a dull-red heat. It was these ditches with red-hot bottoms which, in the darkness of the night, had presented the singular spectacle I described as having witnessed on the evening before.
At one extremity of this oval plain there was a small cone, from which the eruptions before described appeared to issue.
My first step, after examining the few instruments I had brought with me, was to select a spot upon which to measure a base for ascertaining the depth of the crater from its upper edge.
Having decided upon my base line, I took with my sextant the angle of elevation of the rim of the crater above a remarkable spot on a level with my eye. Then fixing my walking-stick into a little crack in the scoria, I proceeded to measure with a tape a base line of 340 feet. Arrived at this point, I again took the angle of elevation of the same part of the rim from the same remarkable spot on a level with the eye. Then, by way of verification, I remeasured my base line and found it only differed from the former measure by somewhat less than one foot. But my walking-stick, which had not penetrated the crack more than a few inches, was actually in flames.
Having noted down these facts, including the state of the thermometer and barometer, in my pocket-book, I took first a survey and then a tour about my fiery domain. I afterwards found, from the result of this measurement, that our base line was 570 feet below one of the lowest points of the edge of the crater. Having collected a few mineral specimens, I applied myself to observe and register the eruptions of the little embryo volcano at the further extremity of the elliptical plain.
These periodical eruptions interested me very much. I proceeded to observe and register them, and found they occurred at tolerably regular intervals. At first, I performed this operation at a respectful distance and out of the reach of the projected red-hot scoria. But as I acquired confidence in their general regularity, I approached from time to time more nearly to the little cone of scoria produced by its own eruptions.
I now perceived an opening in this little cone close to the perpendicular rock of the interior of the great crater. I was very anxious to see real fluid lava; so immediately after an eruption, I rushed to the opening and thus got within the subsidiary crater. But my curiosity was not gratified, for I observed, about forty or fifty feet below me, a huge projecting rock, which being somewhat in advance, effectively prevented me from seeing the lava lake, if any such existed. I then retreated to a respectful distance from this infant volcano to wait for the next explosion.
I continued to note the intervals of time between these jets of red-hot matter, and found that from ten to fifteen minutes was the range of the interval of repose. Having once more reconnoitred the descent into the little volcano, I seized the opportunity of the termination of one of the most considerable of its eruptions to run towards the gap and cautiously to pick my way down to the rock which hid from me, as I supposed, the liquid lava. I was armed with two phials, one of common smelling salts, and the other containing a solution of ammonia. On reaching the rock, I found it projected over a lake which was really filled by liquid fiery lava. I immediately laid myself down, and looking over its edge, saw, with great delight, lava actually in a state of fusion.
Presently I observed a small bubble swelling up on the surface of the fluid lava: it became gradually larger and larger, but did not burst. I had some vague suspicion that this indicated a coming eruption; but on looking at my watch, I was assured that only one minute had elapsed since the termination of the last. I therefore watched its progress; after a time the bubble slowly subsided without breaking.
I now found the heat of the rock on which I was reposing, and the radiation from the fluid lava, almost insupportable, whilst the sulphurous effluvium painfully affected my lungs. On looking around, I fortunately observed a spot a few feet above me, from which I could, in a standing position, get a better view of the lake, and perhaps suffer less inconvenience from its vapours. Having reached this spot, I continued to observe the slow formation and absorption of these vesicles of lava. One of them soon appeared. Another soon followed at a different part of the fiery lake, but, like its predecessor, it disappeared as quietly.
Another swelling now arose about half way distant from the centre of the cauldron, which enlarged much beyond its predecessors in point of size. It attained a diameter of about three feet, and then burst, but not with any explosion. The waves it propagated in the fiery fluid passed on to the sides, and were thence reflected back just as would have happened in a lake of water of the same dimensions.
This phenomenon reappeared several times, some of the bubbles being considerably larger in size, and making proportionally greater disturbance in the liquid of this miniature crater. I would gladly have remained a longer time, but the excessive heat, the noxious vapours, and the warning of my chronometer forbade it. I climbed back through the gap by which I had descended, and rushed as fast as I could to a safe distance from the coming eruption.
I was much exhausted by the heat, although I suffered still greater inconvenience from the vapours. From my observations of the eruptions before my descent into this little crater, I had estimated that I might safely allow myself six minutes, but not more than eight, if I descended into the crater immediately after an eruption.
If my memory does not fail me, I passed about six minutes in examining it, and the next explosion occurred ten minutes after the former one. On my return to Naples I found that a pair of thick boots I had worn on this expedition were entirely destroyed by the heat, and fell to pieces in my attempt to take them off.
On my return from the pit of burning fire, I sat down with my companion to refresh myself with a few biscuits contained in our basket. Cold water would have been the most refreshing fluid we could have desired, but we had none, and my impatient friend cried out, "I wish I had a glass of whisky!" It immediately occurred to me to feel in my own basket for a certain glass bottle preserved in a tight leather case, which fortunately being found, I presented to my astonished friend, with the remark that it contained half a pint of the finest Irish whisky. This piece of good luck for my fellow-traveller arose not from my love but from my dislike of whisky. Shortly before my Italian tour I had been travelling in the north of Ireland, and having exhausted my brandy, was unable to replace it by anything but whisky, a drink which I can only tolerate under very exceptional circumstances.
During my residence at Naples in 1828, the government appointed a commission of members of the Royal Academy of Naples to visit Ischia and make a report upon the hot springs in that island. Being a foreign member of the Academy, they did me the honour of placing my name upon that commission. The weather was very favourable, the party was most agreeable, and during three or four days I enjoyed the society of my colleagues, the delightful scenery, and the highly interesting natural phenomena of that singular island.
None of the hot springs were deep: in several we made excavations which, in all cases, gave increased heat to the water. In one or two, I believe if we had excavated to a small depth or bored a few feet, we might have met with boiling water.
I took the opportunity of this visit to view the devastations made by the recent earthquake in the small town which had been destroyed.
The greater part of the town consisted of narrow streets formed by small houses built of squared stone. In some of these streets the houses on one side were thrown down, whilst those a few feet distant, on the opposite side, although severely damaged, had their walls left standing.
The landlord of the hotel at which we took up our quarters assured me the effects of the recent earthquake were entirely confined to a small portion of the island which he pointed out from the front of his hotel, and added that it was scarcely felt in other parts.
At the commencement of this chapter I mentioned that I had never been consciously sensible of the occurrence of an earthquake. I think it may perhaps be useful to state that on a recent occasion I really perceived the effects of an earthquake, although at the time I assigned them to a different cause.
On the 6th of last October, about half-past three, a.m., most of the inhabitants of London who were awake at that hour perceived several shocks of an earthquake. I also was awake, although not conscious of the shocks of an earthquake.
As soon as I read of the event in the morning papers, I was forcibly struck by its coincidence with my own observations, although I had attributed to them an entirely different cause. In order to explain this, it is necessary to premise that I had on a former occasion instituted some experiments for the purpose of ascertaining how far off the passing of a cart or carriage would affect the steadiness of a star observed by reflection. Amongst other methods, I had fixed a looking-glass of about 12 by 16 inches, by a pair of hinges, to the front wall of my bedroom. It was usually so placed that, as I lay in bed, at the distance of about 10 or 12 feet, I could see by reflection a small gas-light burner, which was placed on my left hand.
By this arrangement any tremors propagated through the earth from passing carriages would be communicated to the looking-glass by means of the front wall of the house, which rose about 40 feet from the surface. The image of the small gas-burner reflected in the looking-glass would be proportionally disturbed. In this state of things, at about half-past three o'clock of the morning in question, I observed the reflected image of the gas-light move downwards and upwards two or three times. I then listened attentively, expecting to hear the sound of a distant carriage or cart. Hearing nothing of the kind, I concluded that the earth wave had travelled beyond the limit of the sound wave, arising from the carriage which produced it. Presently the image of the gaslight again vibrated up and down, and then suddenly fell about four or five inches lower down in the glass, where it remained fixed for a time. Still thinking the observation of no consequence, I shut my eyes, and after perhaps another minute, again saw the image in its lower position. It then rose to its former position, vibrated, and shortly again descended: it remained down for some time and then resumed its first position.
An opportunity presented itself several years after my examination of Vesuvius of witnessing another form under which fire occasionally exerts its formidable power.
I was visiting a friend at Merthyr Tydfil, who possessed very extensive coal-mines. I inquired of my host whether any fire-damp existed in them. On receiving an affirmative answer, I expressed a wish to become personally acquainted with the miner's invisible but most dangerous enemy. Arrangements were therefore made for my visit to the subterranean world on the following day. Professor Moll of Utrecht, who was also a guest, expressed a wish to accompany me.
The entrance to the mine is situated in the side of a mountain. Its chief manager conducted our expedition to visit the 'fire-king.'
We found a coal-waggon drawn by a horse, and filled with clean straw, standing on the railway which led into the workings.
The manager, Professor Moll, and myself, together with two or three assistants, with candles, lanterns, and Davy-lamps, got into this vehicle, which immediately entered the adit of the mine. We advanced at a good pace, passing at intervals doors which opened on our approach and then instantly closed. Each door had an attendant boy, whose duty was confined to the regulation of his own door.
Many were the doors we passed before we arrived at the termination of the tram-road. After travelling about a mile and a half, our carriage stopped and we alighted. We now proceeded on foot, each carrying his own candle, until we reached a kind of chamber where one of our attendants was left with the candles.
We, each holding a Davy-lamp in our hand, advanced towards a small opening in the side of this chamber, which was so low that we were compelled to crawl, one after another, on our hands and knees. A powerful current of air rushed through this small passage. On reaching the end of it, we found ourselves in a much larger chamber from which the coal had been excavated. At a little distance opposite to the path by which we entered was a continuation of the same narrow hole which had led us to the waste in which we now stood. From this opening issued the powerful stream of air which seemed to pass in a direct course from one opening to the other.
On our right hand the large chamber we had entered appeared to spread to a very considerable distance, its termination being lost in darkness. The floor was covered with fragments which had fallen from the roof; so that, besides the risk from explosion, there was also a minor one arising from the possible fall of some huge mass of slate from the roof of the excavation beneath which we stood: an accident which I had already witnessed in the waste of another coal-mine. As we advanced over this flaky flooring it was evident that we were making a considerable ascent. We, in fact, now occupied a vast cavern, which had been originally formed by the extraction of the coal, and then partially filled up by the falling in from time to time of portions of the slaty roof.
As we advanced cautiously with our Davy-lamps beyond the current of air which had hitherto accompanied us, it was evident that a change had taken place in their light: for the flames became much enlarged. Professor Moll and myself mounted a huge heap of these fragments, and thus came into contact with air highly charged with carburetted hydrogen. At this point there was a very sensible difference in the atmosphere, even by a change of three feet in the elevation of the lamp.
Holding up the lamp at the level of my head, I could not see the wick of the lamp, but a general flame seemed to fill the inside of its wire-covering. On lowering it to the height of my knee, the wick resumed its large nebulous appearance.
My companion, Professor Moll, was very much delighted with this experiment. He told me he had often at his lectures explained these effects to his pupils, but that this was the first exhibition of them he had ever witnessed in their natural home.
Although well acquainted with the miniature explosions of the experimentalist, I found it very difficult to realize in my own mind the effects which might result from an explosion under the circumstances in which we were then placed. I inquired of the manager, who stood by my side, what would probably be the effect, if an explosion were to take place? Pointing to the vast heap of shale from which I had just descended, he said the whole of that would be blown through the narrow channel by which we entered, and every door we had passed through would be blown down.
We now retraced our steps, and crawling back through the narrow passage, rejoined our carriage, and were rapidly conveyed to the light of day.
- The late Sir John J. Guest, Bart