“If the history of the earth’s tides should one day be written by some observer of the universe, it would no doubt be said that they reached their greatest grandeur and power in the younger days of Earth, and that they slowly grew feebler and less imposing until one day they ceased to be.”

Why is it great? Few authors have written as magnificently about nature as Rachel Carson, and this sentence is a good example.  Its strength is not in form but content.  It revealed to me something I did not know -- that at one time in the history of Earth, the tides were much more powerful than they are today. They have grown weaker (as a result of the moon drifting farther from Earth, as it turns out, decreasing its gravitational influence), and they will grow weaker and weaker over millions of years until one day they will cease to be. That shocking phrase at the end is the result of a distinctive writing strategy.  I'll call it "the impossible narrator." Look at the premise at the beginning: A history of tides will be written "by some observer of the universe." Who is such an observer?  God?  An alien creature? An earthling who has migrated to another galaxy?  It does not matter.  What matters is that Carson found an elegant vehicle for communicating an amazing reality of the cosmos. (Editor's note: This has been excerpted from Clark's most recent book, "The Art of X-Ray Reading:  How the Secrets of 25 Great Works of Literature Will Improve Your Writing.")