Yesterday morning we breakfasted early at Falmouth, and before 9 started towards Gwennap. I had ascertained on Thursday that John Williams (the senior of a very wealthy and influential family in this country) was probably returned from London. So we drove first to his house Burntcoose or Barncoose, and found him and his wife at home. (They are Quakers, the rest of the family are not.) Sedgwick, and Whewell, and I, or some of our party including me, had slept once at their house. They received George and me most cordially, and pressed us to come and dine with them after our visit to Tresavean mine, of which intention I spoke in my last letter: so I named 4 o'clock as hour for dinner. After a little stay we drove to Tresavean, where I found the Captain of the mine prepared to send an Underground Captain and a Pit-man to descend with us. So we changed our clothes and descended by the ladders in the pumpshaft. Pretty work to descend with the huge pump-rods (garnished with large iron bolts) working violently, making strokes of 12 feet, close to our elbows; and with a nearly bottomless pit at the foot of every ladder, where we had to turn round the foot of the ladder walking on only a narrow board. However we got down to the bottom of the mine with great safety and credit, seeing all the mighty machinery on the way, to a greater depth than I ever reached before, namely 1900 feet. From the bottom of the pump we went aside a short distance into the lowest workings where two men nearly naked were driving a level towards the lode or vein of ore. Here I felt a most intolerable heat: and upon moving to get out of the place, I had a dreadful feeling of feebleness and fainting, such as I never had in my life before. The men urged me to climb the ladders to a level where the air was better, but they might as well have urged me to lift up the rock. I could do nothing but sit down and lean fainting against the rocks. This arose entirely from the badness of the air. After a time I felt a trifle better, and then I climbed one short ladder, and sat down very faint again. When I recovered, two men tied a rope round me, and went up the ladder before me, supporting a part of my weight, and in this way I ascended four or five ladders (with long rests between) till we came to a level, 260 fathoms below the adit or nearly 300 fathoms below the surface, where there was a tolerable current of pretty good air. Here I speedily recovered, though I was a little weak for a short time afterwards. George also felt the bad air a good deal, but not so much as I. He descended to some workings equally low in another place (towards which the party that I spoke of were directing their works), but said that the air there was by no means so bad. We all met at the bottom of the man-engine 260 fathoms below the adit. We sat still a little while, and I acquired sufficient strength and nerve, so that I did not feel the slightest alarm in the operation of ascending by the man-engine.