Three Metaphors in Two Ways of Seeing a River
Two Ways of Seeing a River by Mark Twain
What the first responder gave you are known as similes which are basically the same as metaphors (in the way that they compare two things) except they use like or as.
Metaphors can be vague and open to interpretation.
The river itself is clearly a metaphor, as to what it is a metaphor for is unclear to me.
I believe that each reader will choose as to what this metaphor means for themselves (and I think that will be based on experiences that they had in life).
To me the river is either life itself or perhaps more likely an experience in life (notice how he says it's unfamiliar from what he is used to at home). To me this speaks of a life experience perhaps a journey or maybe even a relationship.
One thing is clear and that is that what he is talking about he was excited to learn about at first, he was very focused and determined to learn more about it, this experience (whatever it may be) is something that was once of great interest to him. It intrigued him, astonished him and I might go as far to say he had some love/hope/belief for it at some point in time.
But as he "mastered" it or perhaps grew some knowledge about this river it started to loose it's magic. If the river is life I can see what he's saying, as I look at my niece she is filled with joy, she's untouched by the world, innocent, she's too young to understand a lot of things that happen. I noticed, myself, that as I grew older I began to question more, the more questions the more knowledge. I can't help but feel the more I know the more I loose of what my niece has (whatever this essence or river of hers is). It would seem, in my opinion, that as we grow older, life can loose the magic it once had.
Have you ever seen tourists in your area? they are fascinated by the attractions, they want to see them all and perhaps at one time locals did too, but as time goes by we hardly notice them or acknowledge their importance/significance anymore. They loose their luster over time because they simply "are" and exist. Or go travel and see the graffiti and trash on the Eiffel tower, the Roman arenas, castles and such. I was surprised to see that myself but it's similar to how I was once astonished by the beauty of Pikes Peak and now I guess I hardly notice it. From time to time, rarely, I will notice the beauty of the mountains again and I'll sit there and examine them. But to be truthful more often I just go about life as if they aren't even there, my focus is elsewhere.
And that distraction may very well be the steamboat or the compass (this would be another metaphor). The compass to me stands for the conformity of life, we all grow up, get jobs, make money, pay taxes, etc. etc. etc. It can all be just so, I don't know, normal I guess. It's almost like were being pointed at an office or a cubicle. It's safe. Safe piloting. You know what I mean? it's kind of hard to explain.
The doctors may very well be yet another metaphor, ever since he lost the majesty of the river he has "pitied doctors from his heart." To me the doctors are society. They want to "fix" him, fix his heart, but he won't allow it and in fact he pities them for their beliefs and trying to make him come back to a falsehood. They don't see the beauty anymore (notice how the doctors analyze the ripples as simple "breaks" in the water, everything has become scientific, having no beauty no majesty). These "doctors" they too are masters of the river because they know so much that they miss the simple beauty of it.
That's 3, if you spent more time on it you could surely find several more, I'm sure of it.