But I must tell you what this tunnel is like, or at least try to do so. You enter, by flights of stairs, the first door, and find yourself on a circular platform which surrounds the top of a well or shaft, of about two hundred feet in circumference and five hundred in depth. This well is an immense iron frame of cylindrical form, filled in with bricks; it was constructed on level ground, and then, by some wonderful mechanical process, sunk into the earth. In the midst of this is a steam engine, and above, or below, as far as your eye can see, huge arms are working up and down, while the creaking, crashing, whirring noises, and the swift whirling of innumerable wheels all round you, make you feel for the first few minutes as if you were going distracted. I should have liked to look much longer at all these beautiful, wise, working creatures, but was obliged to follow the last of the party through all the machinery, down little wooden stairs and along tottering planks, to the bottom of the well. On turning round at the foot of the last flight of steps through an immense dark arch, as far as sight could reach stretched a vaulted passage, smooth earth underfoot, the white arches of the roof beyond one another lengthening on and on in prolonged vista, the whole lighted by a line of gas lamps, and as bright, almost, as if it were broad day. It was more like one of the long avenues of light that lead to the abodes of the genii in fairy tales, than anything I had ever beheld. The profound stillness of the place, which was first broken by my father's voice, to which the vaulted roof gave extraordinary and startling volume of tone, the indescribable feeling of subterranean vastness, the amazement and delight I experienced, quite overcame me, and I was obliged to turn from the friend who was explaining everything to me, to cry and ponder in silence. How I wish you had been with us, dear H----! Our name is always worth something to us: Mr. Brunel, who was superintending some of the works, came to my father and offered to conduct us to where the workmen were employed--an unusual favor, which of course delighted us all. So we left our broad, smooth path of light, and got into dark passages, where we stumbled among coils of ropes and heaps of pipes and piles of planks, and where ground springs were welling up and flowing about in every direction, all which was very strange. As you may have heard, the tunnel caved in once, and let the Thames in through the roof; and in order that, should such an accident occur again, no lives may be lost, an iron frame has been constructed--a sort of cage, divided into many compartments, in each of which a man with his lantern and his tools is placed--and