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 {209} 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.
〈SENSATIONS IN A DIVING-BELL.〉
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 {210} 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.
〈OBSERVATION IN DIVING BELL.〉
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 {211} 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.