On the invitation of Colonel Paine and Engineer Cottingwood, I was one of a party of four to descend into the caisson to examine its workings and inspect its machinery. Arriving at the foot of Roosevelt Street, we found indications of the construction of a large building. There were numerous derricks, scaffoldings, and building materials in the vicinity, and every where there was activity. Just as we reached the works we found a gang of sixty men indulging in hot coffee, which is always served to them previous to their descending the shaft of the caisson. Their coffee drinking over, and the roll-call answered, they walked in single file to the mouth of the shaft, and there waited the arrival of those whom they were about relieving. Most of the men wore nothing but their shirts and trousers, with water-proof boots reaching above the knees. At a signal given by the foreman of the gang, some of them entered an elevator, while others proceeded down a spiral staircase, and were soon lost to view. Before taking the reader to the interior of the caisson, it may be well to state that it is nothing else than a large box of iron and wood, the full size of the intended abutment. This box is turned bottom upward, and rests upon its edges. [Sidenote: DESCRIPTION OF THE CAISSON.] It is one hundred and two feet wide, and one hundred and seventy-two feet long, and nearly ten feet in height. Its immense weight is supported by several solid trusses of oak and iron, which run across the caisson; and in addition to this, it receives an upward support of forced air equal to forty thousand tons. The pressure of the air in the caisson is forty-four pounds to the square inch, being twenty-nine pounds more than the ordinary atmospheric pressure. The air is sent down the caisson by means of pumps, there being fourteen engines, each of twenty-four horse power, constantly at work. In the centre of the caisson, an entrance is obtained by means of a shaft having a spiral staircase of over one hundred circular steps, and there is another entrance by an elevator, which, by the by, is the most agreeable way of descending, particularly if the visitor is inclined to corpulence. It was down this entrance I went with the rest of our party. Like the workmen, each of us swallowed a small quantity of hot coffee and biscuit, as we were told that we should suffer less from the effects of the descent. Under the direction of our guide, we took our stand inside the elevator, for the simple reason that we could not sit. There were no velvet-covered seats, as are generally found in hotel elevators. [Sidenote: GOING INTO THE INTERIOR.]