Passages from the Life of a Philosopher/Chapter XV
experience by water.
Shooting Sea-birds—Walking on the Water—A Screw being loose—The Author nearly drowned—Adventure in the Thames Tunnel—Descent in a Diving-bell—Plan for Submarine Navigation.
The grounds surrounding my father's house, near Teignmouth, extended to the sea. The cliffs, though lofty, admitted at one point of a descent to the beach, of which I very frequently availed myself for the purpose of bathing. One Christmas when I was about sixteen I determined to see if I could manage a gun. I accordingly took my father's fowling-piece, and climbing with it down to the beach, I began to look about for the large sea-birds which I thought I might have a chance of hitting.
I fired several charges in vain. At last, however, I was fortunate enough to hit a sea-bird called a diver; but it fell at some distance into the sea: I had no dog to get it out for me; the sea was rough, and no boat was within reach; also it was snowing.
So I took advantage of a slight recess in the rock to protect my clothes from the snow, undressed, and swam out after my game, which I succeeded in capturing. The next day, having got the cook to roast it, I tried to eat it; but this was by no means an agreeable task, so for the future I left the sea-birds to the quiet possession of their own dominion.
Shortly after this, whilst residing on the beautiful banks of the Dart, I constantly indulged in swimming in its waters. One day an idea struck me, that it was possible, by the aid of some simple mechanism, to walk upon the water, or at least to keep in a vertical position, and have head, shoulders, and arms above water.
My plan was to attach to each foot two boards closely connected together by hinges themselves fixed to the sole of the shoe. My theory was, that in lifting up my leg, as in the act of walking, the two boards would close up towards each other; whilst on pushing down my foot, the water would rush between the boards, cause them to open out into a flat surface, and thus offer greater resistance to my sinking in the water.
I took a pair of boots for my experiment, and cutting up a couple of old useless volumes with very thick binding, I fixed the boards by hinges in the way I proposed. I placed some obstacle between the two flaps of each book to prevent them from approaching too nearly to each other so as to impede their opening by the pressure of the water.
I now went down to the river, and thus prepared, walked into the water. I then struck out to swim as usual, and found little difficulty. Only it seemed necessary to keep the feet farther apart. I now tried the grand experiment. For a time, by active exertion of my legs, I kept my head and shoulders above water and sometimes also my arms. I was now floating down the river with the receding tide, sustained in a vertical position with a very slight exertion of force.
But unfortunately one pair of my hinges got out of order, and refused to perform its share of the propulsion. The result was that I became lop-sided. I was therefore obliged to swim, which I now did with considerable exertion; but another difficulty soon occurred,—the instrument on the disabled side refused to do its share in propelling me. The tide was rapidly carrying me down the river; my own exertions alone would have made me revolve in a small circle, consequently I was obliged to swim in a spiral. It was very difficult to calculate the curve I was describing upon the surface of the water, and still more so to know at what point, if at any, I might hope to reach its banks again. I became very much fatigued by my efforts, and endeavoured to relieve myself for a time by resuming the vertical position.
After floating, or rather struggling for some time, my feet at last touched the bottom. With some difficulty and much exertion I now gained the bank, on which I lay down in a state of great exhaustion.
This experiment satisfied me of the danger as well as of the practicability of my plan, and ever after, when in the water, I preferred trusting to my own unassisted powers.
At the close of the year 1827, as I anticipated a long absence from England, I paid a visit to the Thames Tunnel, in the construction of which I took a great interest. My eldest son, then about twelve years of age, accompanied me in this visit. I fortunately found the younger Brunel at the works, who kindly took us with him into the workings.
We stood upon a timber platform, distant about fifty feet from the shield, which was full of busy workmen, each actively employed in his own cell. As we were conversing together, I observed some commotion in the upper cell on the right hand side. From its higher corner there entered a considerable stream of liquid mud. Brunel ran directly to the shield, a line of workmen was instantly formed, and whatever tools or timber was required was immediately conveyed to the spot.
I observed the progress with some anxiety, since but a short time before a similar occurrence had been the prelude to the inundation of the whole tunnel. I remained watching the fit time, if necessary, to run away; but also noticing what effect the apparent danger had on my son. After a short time it was clear that the ingress of liquid mud had been checked, and in a few minutes more Brunel returned to me, having this time succeeded in stopping up the breach. I then inquired what was really the nature of the danger we had escaped. Brunel told me that unless himself or Gravatt had been present, the whole tunnel would in less than ten minutes have been full of water. The next day I embarked for Holland, and in about a week after I read in Galignani's newspaper, that the Thames had again broken into the tunnel; that five or six of the workmen had been drowned, and that Brunel himself had escaped with great difficulty by swimming.
In 1818, during a visit to Plymouth, I had an opportunity of going down in a diving-bell: I was accompanied by two friends and the usual director of that machine.
The diving-bell in which I descended was a cast-iron vessel about six feet long by four feet and a half wide, and five feet eight inches high. In the top of the bell there were twelve circular apertures, each about six inches in diameter, filled by thick plate-glass fixed by water-tight cement. Exactly in the centre there were a number of small holes through which the air was continually pumped in from above.
At the ends of the bell are two seats, placed at such a height, that the top of the head is but a few inches below the top of the bell; these will conveniently hold two persons each. Exactly in the middle of the bell, and about six inches above its lower edge, is placed a narrow board, on which the feet of the divers rest. On one side, nearly on a level with the shoulders, is a small shelf, with a ledge to contain a few tools, chalk for writing messages, and a ring to which a small rope is tied. A board is connected with this rope; and after writing any orders on the board with a piece of chalk, on giving it a pull, the superintendent above, round whose arm the other end of the rope is fastened, will draw it up to the surface, and, if necessary, return an answer by the same conveyance.
In order to enter the bell, it is raised about three or four feet above the surface of the water; and the boat, in which the persons who propose descending are seated, is brought immediately under it; the bell is then lowered, so as to enable them to step upon the foot-board within it; and having taken their seats, the boat is removed, and the bell gradually descends to the water.
On touching the surface, and thus cutting off the communication with the external air, a peculiar sensation is perceived in the ears; it is not, however, painful. The attention is soon directed to another object. The air rushing in through the valve at the top of the bell overflows, and escapes with a considerable bubbling noise under the sides. The motion of the bell proceeds slowly, and almost imperceptibly; and, on looking at the glass lenses close to the head, when the top of the machine just reaches the surface of the water, it may be perceived, by means of the little impurities which float about in it, flowing into the recesses containing the glasses. A pain now begins to be felt in the ears, arising from the increased external pressure; this may sometimes be removed by the act of yawning, or by closing the nostrils and mouth, and attempting to force air through the ears. As soon as the equilibrium is established the pain ceases, but recommences almost immediately by the continuance of the descent. On returning, the same sensation of pain is felt in the ears; but it now arises from the dense air which had filled them endeavouring, as the pressure is removed, to force its way out.
If the water is clear, and not much disturbed, the light in the bell is very considerable; and, even at the depth of twenty feet, was more than is usual in many sitting-rooms. Within the distance of eight or ten feet, the stones at the bottom began to be visible. The pain in the ears still continues to occur at intervals, until the descent of the bell terminates by its resting on the ground. The light is sufficient, after passing through twenty feet of sea water, even for delicate experiments; and a far less quantity is enough for the work which is usually performed in those situations.
The temperatures of the hand and of the mouth, under the tongue, were measured by a thermometer, but they did not seem to differ from those which had been determined by the same instrument previous to the descent; at least, the difference did not amount to one-sixth of a degree of Fahrenheit's scale. The pulse was more frequent.
A small magnetic needle did not appear to have entirely lost its directive power, when placed on the footboard in the middle of the bell; but its direction was not the same as that which it indicated on shore. This was determined by directing, by means of signals, the workmen above to move the bell in the direction of one of the co-ordinates; a stick then being pressed against the bottom drew a line parallel to that co-ordinate, its direction by compass was ascertained in the bell, and the direction of the co-ordinate was determined on returning to the surface after leaving the bell.
Signals are communicated by the workmen in the bell to those above, by striking against the side of the bell with a hammer. Those most frequently wanted are indicated by the fewest number of blows; thus a single stroke is to require more air. The sound is heard very distinctly by those above; but, it must be confessed, that to persons unaccustomed to it, the force with which a weighty hammer is driven against so brittle a material as cast iron is a little alarming.
After ascending a few inches from the bottom, the air in the bell became slightly obscured. At the distance of a few feet this appearance increased. Before it had half reached the surface, it was evident that the whole atmosphere it contained was filled with a mist or cloud, which at last began to condense in large drops on the whole of the internal surface.
The explanation of this phenomenon seems to be, that on the rising of the bell the pressure on the air within being diminished by a weight equal to several feet of water, it began to expand; and some portion of it escaping under the edges of the bell, reduced the temperature of that which remained so much, that it was unable to retain, in the state of invisible vapour, the water which it had previously held in solution. Thus the same principle which constantly produces clouds in the atmosphere filled the diving-bell with mist.
This first led me to consider the much more extensive question of submarine navigation. I was aware that Fulton had already descended in a diving-vessel, and remained under water during several hours. He also carried down a copper sphere containing one cubic foot of space into which he had forced two hundred atmospheres. With these means he remained under water and moved about at pleasure during four hours.
But a closed vessel is obviously of little use for the most important purposes to which submarine navigation would be applied in case of war. In the article Diving Bell, published in 1826, in the 'Encyclopedia Metropolitana,' I gave a description and drawings of an open submarine vessel which would contain sufficient air for the consumption of four persons during more than two days. A few years ago, I understand, experiments were made in the Seine at Paris, on a similar kind of open diving-vessel. Such a vessel could be propelled by a screw, and might enter, without being suspected, any harbour, and place any amount of explosive matter under the bottoms of ships at anchor.
Such means of attack would render even iron and iron-clad ships unsafe when blockading a port. For though chains were kept constantly passing under their keels, it would yet be possible to moor explosive magazines at some distance below, which would effectually destroy them.