« PreviousContinue »
and, enchanted by the success of his contrivance, he intimates the he might, perhaps, have tarried there all his life, if he had like Instead, however, of renovating the air by mechanical means, SL persons have proposed to restore it to purity by chemical proces Cornelius van Drebbell (better known as the inventor of the thes mometer) is said to have possessed some plan by which he could rent the tainted atmosphere of a submarine vessel ; and, in proof of the he went down with some rowers in the Thames, and remained under water for a considerable period. And does not Father Mersenne spest of a French diver, one Barricus by name, who could continue submerged for six hours together (and burn a candle to boot), with only a cubic foot or two of air at his disposal—though it is known that during this interval, the contents of fourteen or fifteen hogsheads woul: be required for the service of a single pair of lungs? Mr. Babbar suggested that the carbonic acid emitted by the pulmonary ons might be fixed by means of lime or ammonia in solution ; and that condensed oxygen might be hoarded up for the renewal of the ats sphere of the machine.
By this time we are fairly in the water, and I observe that you curry your fingers to your ears, and look as if you were rather troublel 2 that region. It is the same with myself. We begin to complain of a horrible pressure upon our “drums." We are both of opinion thes they will give way in case we are not speedily relieved. We feel, indeed, as if some invisible sprite were thrusting quills into the apesar passages. The philosophy of the nuisance is this, the atmosphere the bell necessarily grows denser as we descend, because it is creador into smaller compass by the increasing weight of the water ; QUE quently, as the air within the cavities of the ear is thinner than the without, the intervening membrane will be cruelly stretched, it misli possibly be ruptured, unless the equilibrium were restored 19 10 occasion, a diver attempted to protect himself by filling the external chambers with chewed paper ; but on arriving at the surface, he fel that the pieces had been wedged in so forcibly that they were exinced with considerable difficulty. Fortunately the remedy is very simple You must pretend to swallow air as you would swallow soup In b act of deglutition, the condensed fluid around you finds almise a through the eustachian tube to the interior of the organs, and thus by equalizing the pressure on both sides of the tympanum the pain is me moved. But this process must be repeated at intervals as we atrand and similarly when we return-I hope we shall return-though the conditions are then reversed. It is decidedly not pleasant to feel as a quill were poked into your ear at each step of your progress
We proceed slowly. Perhaps you think the men who are lowering us are anxious to make the most of our agony. It certainly lusk. Tery like it; but there is one good reason at least why we should unk in a leisurely fashion. Triewald mentions a diver who was let duwa jac pitately for the space of a fathom, owing to the carelessness of the people who worked the bell. The result was, that the rapid cundcase
tion of the air forced the blood out of his nose and ears, and compressed his body as if it had been suddenly loaded with lead. Let us hope, therefore, that the men will be particularly cautious on this point, for a run of a few feet would be highly objectionable.
What is that you say? It is growing excessively hot, you think. Undoubtedly. This is another consequence of the pressure to which our little atmosphere is exposed. Air contains a quantity of caloric, which may be squeezed out of it as water is squeezed out of a sponge. Let a piece of fine tinder be placed in a tube closed at one extremity, and provided with a piston at the other; give a smart blow to the latter, and sufficient heat will be developed to inflame the susceptible material. Were the atmosphere of our globe suddenly and extensively compressed, its caloric would be expelled so copiously that it might set fire to every combustible thing, and melt or vitrify the whole surface. Besides, as the warmer and lighter air always ascends, the upper portion of the bell (the place where our heads are at present stationed) must necessarily be the hottest latitude in the machine. You begin to fear, therefore, that you will probably faint ; and you wish to know whether my sensations are the same. I will give you an explicit reply. I scorn to use any disguise. I have the honour to feel equally uneasy with yourself; and I candidly confess my apprehensions that if the temperature should continue to rise until it reaches the swooning point (unmarked on most thermometers), our friends on terra firma may have reason to regret that we have ever ventured upon this perilous enterprise.
Remembering, however, that fainting has become quite unfashionable, and that we are all strong-minded men and women now-a-days, I make a vigorous effort to master my emotions, and request your attention to the fact that whilst the air appears to grow hotter the water in reality becomes cooler. For, as the warmer, and consequently the lighter, fluid (down to about 40° F.) must float upon the heavier, the sea will gradually increase in chilliness until (if deep enough) a certain point is attained ; so that even within the tropics, where a blazing sun is playing upon the surface of the ocean, water has been hoisted up from below at a temperature not many degrees above the freezing point. And here, also, I am reminded of another little philosophical peculiarity of our position. Your voice sounds rather thin and feeble ; and I notice that you do not seem to catch my words as distinctly as might be expected, considering that we are in such friendly proximity. How is this? It is well known that the loudness of a sound is affected by the density or tenuity of the air. Every person who has read Joyce's “ Scientific Dialogues,” or “ Brewer's Guides” is presumed to be aware of the fact that when a bell is rung in the receiver of an air-pump, the noise grows fainter as the winch is worked, until at length you see the clapper wag, but hear no merry tinkle. The converse should, of course, obtain if the atmosphere is compressed ; and hence a pistol, which would produce an explosion like that of a cracker on the top of a high mountain, ought to go off like a little cannon when discharged in a
diving-machine. Long ago, however, it was ascertained by M. Collade that men did not talk like Stentors whilst descending in the bell, le: seemed to roar pretty much like Bottom's sucking doves. Man ascribes this apparent anomaly to the fact first indicated by I: Wollaston, that when the membrana tympani is rendered tense from any cause, partial deafness is produced. So long as the acoustic : tain is strained by atmospheric pressure on either side, the faculty." hearing is impaired; but, of course, when it recovers it natural lanit and is at peace within and without, the increased density of the air be recognized in its gonorous results.
Talking of sound, however (and I do not think it beneath me acknowledge that I turn philosophical for the purpose of kopping " my courage, and of diverting my attention from the horrors of " position), you must observe that a noise will travel with greater Isrilas through water, when excited in that fluid, than it does through air. Colladon found that a bell could be distinctly heard across Lak Leman, a distance of nine miles, when the vibrations were transmitte. by a purely liquid route. In fact, they traverse an aqueous la four-and-a-half times faster than they do an atmospheric one. Hence if a merman has anything to say to a mermaid (which, I supine, T. sometimes happen), or if a Triton blows his trumpet to summa the sea-gods to a council (which, I imagine, rarely occur in these unke sical days), the sound will rush along with great velocity, and duf. itself through a sphere of considerable extent. All submarine me versations, as sea-nymphs are well aware, should therefore he care on with caution, if it is important that they should not be overbrand
Meanwhile, we continue to descend inch by inch. The bhi course, becomes dimmer as we procred. Should the water le . " turbid, we are soon shrouded in what Halley calls “ perfict nicht Should it prove tolerably pellucid, we receive a softenedl sort of nal: ance, which is green where the liquid is fresh, blue when it is salt
Ah! what is that I hear ? You don't like the present alle ! things at all; you have a strong objection to darkness, ani partinlarly to darkness in a diving-bell. Why, my dear friend, these sy precisely my own sentiments; but I am afraid we cannot in the signal for recal with any credit, until we have gong a little further in the deep. 'ndoubtedly, if we were to sink as far as a free! trust my tones are not becoming unduly trmulous-srarely a TV the sun, generally speaking, could follow us there. It is ruler that, at a depth of 200 fact, the lustre of that luminary is nu in effect to the light of a farthing candle shining ujum you as ihr Le tance of a foot, Let it not be supposed, however, that the brake the great orb are stripped of their fir and heat by plan ini. a stratum of the coldest water. A workmin employed on the mouth breakwater went down in a diving-boll which had a glass fixed in the top for the purpose of letting in light. 19; unexpectedly operated as a burning lens, for the per teil l e covered that a cont 1 :ration was ruxing on his hal, his page wa
having come into focus, and his scalp being perilled by this touch of solar pleasantry.
And since without light there can be no colour, it has been observed that the hues of animals, which dwell at various depths in the ocean, decline in intensity until a certain limit is reached ; and if, beyond that point, life still exists, it appears to be as pallid and cadaverous as if it were already on the brink of death. The late Professor Edward Forbes established a kind of chromatic scale amongst the Testacea of the Ægean Sea. Ranking them in zones according to their different habitats, he found that the liveliest tints and gayest combinations of colour were to be discovered in the shells which occupied the uppermost, or littoral, belt. Whilst the species near the surface were drenched in prismatic glories, the denizens of the inferior regions grew more modest in their markings and adornments, until at last even the faint flush of colour discernible amongst these creatures seemed to be well-nigh extinguished, and the few specimens which survived were, for the most part, wan and lustreless things. Out of 18 shells raised from a depth of 100 fathoms and upwards in the Mediterranean, only one presented any decided tintings; and, in our own seas, every individual drawn from a similar depth proved to be wholly without hue.
Further and further we continue to sink. The time we have consumed, and let us be frank—the trepidation we have endured, might almost induce us to believe that we had descended some thousands of feet into the watery abyss. And yet a few fathoms will measure the whole distance we have described. Since the height, and consequently the weight of the fluid above us is increasing at every step of our progress, it follows that the space reserved for air within the bell is constantly contracting. You observe that the liquid is gradually rising in the machine. You have had to double up your legs already, I perceive; and if we proceed much deeper we shall be immersed to our chests, and almost strangled in the embrace of the floods. For, at a depth of about thirty-two feet, we are exposed to a pressure equivalent to that of a double atmosphere. In other words, an additional weight of from fourteen to fifteen pounds is put upon every one of our square inches. The same invisible sprite who amuses himself by poking invisible quills into your ears has been silently piling up several hundredweights upon our frames, so that each of us now sustains a burden of more than twenty tons. “What Atlases we must be !" you exclaim. Fortunately there is no vacuum within the body, otherwise it would collapse and shrivel beneath the prodigious incubus. If a diving-apparatus were a closed machine, it might be lowered to a greater depth than an open bell; but it would be necessary to construct it of stout materials in order that it might resist the powerful strain to which it would be exposed. Sir John Herschel mentions an individual (probably Mr. Day) who fitted up a vessel for recovering treasure from sunken ships, and who went down by way of trial, but never returned to the light ; for, as no adequate allowance had been made for the increased pressure of water, the frail fabric was crushed like a band-box in the coils of a boa-constrictor. Or, to put the matter in a more pleasing form, let me recommend you to take a bottie of pure sherry (if such a phenomenon can be discovered in Europe and, having corked and sealed it, send it into the depths of the ocean by means of a sounding line. Haul it up, and take a glass—I beg to decline for myself—and what will be the result ! Why, you will find that a vertical voyage does not improve the quality of wine as a honzontal one is presumed to do. The liquid which went down price sir or seven shillings the bottle will come up at considerably less than a farthing the barrel. The superincumbent weight of the ocean has, in fact, so compressed the cork that the contents will be little better than mere brine. Need I say, therefore, that no merman accustomed to sport in deep waters could ever wear such a head-dress as a terrestrial hat, for it would be forced down upon his skull like an empty egs shell ; and certainly no sea-nymph would dream of employing garments stiffened by crinoline or expanded by slender steel hoops, like their sisterhood of the land.
But here you remind me that a curious question is sometimes raised -occasionally, too, amongst very intelligent people-respecting the effect of deep water upon sinking substances.
What excellent nerves you must have to propound a philosophical thesis at this depth below the surface! Such composure of mind is exceedingly uncommon in a diving-bell. I will endeavour to wimi up my courage to the height of your argument. Now, what is your difficulty ?
This : it has sometimes been contended that as the weight of water constantly increases there must be a point, if the sea be deep enough, whero electric cables will float, and where even cannon-lalls must refuse to sink any further. This conclusion, however, arises from some confusion of idea in regard to pressure and compressibility. If water were a “squeezable" fluid, like the air in the bell, a gira quantity taken from the surface of the ocean-say, a pailful-would be gradually reduced in bulk the lower we descended, until it might be contained in a common tumbler. But in that case its density-hati the quantity of matter included in a determinate space would be proportionately augmented. Now, the only condition on which a colae inch of iron or other heavy substance could remain in suspension as any particular depth, would be that it weighed neither more ncr le than a cubic inch of the surrounding fluid. But it happens that water is virtually an incompressible liquiil. Its particles won't coalment to be forced into closer proximity. The Florentine academicians thought they could subdue its stubbornness by subjecting a sphere u gold filled with the fluid to enormous pressure ; but the drug OURI through the metal rather than compromise their chincter by the slightest concession. Subsequent experiments by Canton, Perkins, and Oersted have indeed shown that there is some sinall contractiva a bulk; but it is so trifling that the last-named philosopher estima it at one part in forty-six millions for each additional atmospher