In the last part of the chapter he talks about the experience. This part of the chapter is famous and parts of it are often quoted. By learning the river the way a pilot knows it,
I had made a valuable acquisition. But I had lost something, too. I had lost something which could never be restored to me while I lived. All the grace, the beauty, the poetry had gone out of the majestic river!
He gives some very evocative descriptions of how the river looked to him, before he knew it as a pilot, and afterwards. He then makes a surprising jump:
Since those days, I have pitied doctors from my heart. What does the lovely flush in a beauty's cheek mean to a doctor but a 'break' that ripples above some deadly disease. Are not all her visible charms sown thick with what are to him the signs and symbols of hidden decay? Does he ever see her beauty at all, or doesn't he simply view her professionally, and comment upon her unwholesome condition all to himself? And doesn't he sometimes wonder whether he has gained most or lost most by learning his trade?
Part 1. I'll see if I can help without actually giving you an answer.
In this chapter and in surrounding chapters Mark Twain is learning to pilot a steamboat. The captain, Mr. Bixby, is teaching him in a challenging way. Here are some key sentences from the chapter, and my comments.
Now I had often seen pilots gazing at the water and pretending to read it as if it were a book... Mr. Bixby seemed to think me far enough advanced to bear a lesson on water-reading....
"See that long slanting line on the face of the water? Now, that's a reef. Moreover, it's a bluff reef... If you were to hit it you would knock the boat's brains out.... Do you see where the line fringes out at the upper end and begins to fade away?"
Bixby is teaching him how to tell if the water is safe for a steamboat or not. You can't see the actual danger, the reef itself. You have to recognize it from the way the water looks over it. This is called "reading" the river. Sometimes "read" can mean "understand something by looking at it."
"Now watch her; watch her like a cat, or she'll get away from you. When she fights strong and the tiller slips a little, in a jerky, greasy sort of way, let up on her a trifle; it is the way she tells you at night that the water is too shoal."
He is coaching Twain on how to guide the boat safely across it. You don't need to understand all of the details of what he is saying. Most readers don't. People with experience in sailing might understand better than I do. We enjoy the realistic way the dialog sounds.
During the afternoon watch the next day, Mr. Bixby asked me if I knew how to run the next few miles. I said--
'Go inside the first snag above the point, outside the next one, start out from the lower end of Higgins's wood-yard, make a square crossing and----'
'That's all right. I'll be back before you close up on the next point.'
Bixby tricks Mark Twain. He sets up a test for him. He knows that a river pilot needs to be resourceful under stress. He first makes sure Twain knows what to do--for the next few miles--and then leaves. Twain expects him to come back and help him before he gets to "the next point."
...he was hiding behind a chimney to see how I would perform...
Bixby knows that past the next point there is a place where the water looks as if there is a dangerous bluff reef, but it is actually safe. So he will get a chance to see what Twain does when he thinks the ship is in danger.
...I went gaily along, getting prouder and prouder,..
Twain feels confident. Overconfident.
...One of those frightful bluff reefs was stretching its deadly length right across our bows!...
Bixby is giving him a lesson... like modern simulator practice... by putting Twain into a situation that looks and feels dangerous but is really safe. He also is giving Twain a lesson on how difficult and how important it is to "read the river," and showing Twain that he still has a lot to learn.